It is the Maharaja of Jodhpur's 68th birthday.

Hundreds of relatives, lesser princes and local dignitaries, all dressed in magnificent finery, flock to the vast Umaid Bhawan palace to pay their respects.

In a voluminous marquee on the expansive lawns, they line up, offer Gaj Singh a monetary token and touch his feet before going outside for a slap-up lunch.

Earlier in the morning, Bapji - as the Maharaja is widely known - had been greeted with similar adulation when he visited his ancestors' tombs below Jodhpur's equally imposing 15th-century Mehrangarh Fort.

Ordinary Jodhpuris had crowded round his silver Mercedes, offering him food, prayers and good wishes. He has worked hard to earn such respect, using his stature to help the city in many ways, but you would never guess that he - like all India's other princes - was officially dethroned by Indira Gandhi in 1971.

I arrived in Rajasthan seven years after that upheaval, fresh from university, to teach at Mayo College in Ajmer, a town 200km east of Jodhpur.

The school was founded by the British in 1875 to educate the sons of the state's princes. Its first student, Maharaja Mangal Singh of Alwar, arrived on an elephant with 200 retainers and assorted horses, camels and tigers.

Mayo soon became known as "the Eton of India" and my father's first cousin, Jack Gibson, was its last British principal - indeed the last resident Brit anywhere in Rajasthan.

It was a magical year. I taught English, produced a play and enjoyed endless sport. On weekends, I would visit the crumbling, bat-infested forts of my newly impoverished students and sleep on the battlements as the smell of cow dung fires drifted up from the mediaeval villages below.

The era of mass tourism had yet to begin, so except for the odd hippie or trailblazing backpacker, I had the wonders of Rajasthan to myself.

Since then, the population of India has more than doubled to 1.3 billion and the economy has taken off, so it was with some apprehension that I return to discover whether - nearly 40 years on - the romantic land of my memory still existed.

Delhi is a horror. Now officially the world's most polluted city, it is covered in a pall of smog that makes my eyes smart and the air smells acrid. The roads are clogged with every conceivable form of transport. Brown dust coats everything - trees, lawns, the Red Fort - muting their colours.

Connaught Place, New Delhi's shopping hub, has been almost entirely colonised by Western designer stores, with the delightful exception of the colonial-era New Delhi Stationery Mart, which still sells fountain pens. It is with some relief that I retreat to the air-conditioned comfort of the Lodhi hotel.

An early morning express train whisks me down to Jaipur. That is also a shock.

I remembered a small, relaxed town. Today, the fabled "Pink City" is a teeming metropolis of six million with a metro, international airport, flyovers and shopping malls.

The exquisite 18th-century Hawa Mahal - the Palace of Winds where royal women could watch the outside world unseen from its famous latticed windows - is packed not just with Westerners, but with a new phenomenon: large numbers of tourists drawn from India's rapidly expanding middle classes.

I retreat to the tranquil Rajasthan polo grounds. I am in luck.

Padmanabh Singh, the 17-year-old Maharaja of Jaipur, is playing. Naturally, he wears No. 1. He scores a goal, though the Jaipur Warriors lost.

Later, I go shopping and discover that not all progress is bad. Unable to choose between three dhurries (hand-woven rugs), the shopkeeper simply sends pictures of them via WhatsApp to my wife in London.

A six-lane highway takes me to Ajmer where a statue of Lord Mayo, a 19th-century Viceroy of India, still stands outside the college that bears his name. A crown still tops the clock tower of the magnificent main school building - all arches, domes and ornate balustrades built of white marble. The 76ha campus is still an oasis of calm where peacocks strut amid the elegant boarding houses and bougainvillea.

But Mayo has changed too. It now has a girls' school, golf course, shooting range, open-air theatre, polo field and stables for 58 horses.

Thankfully, it also employs a proper French teacher. Back in 1978, I was prevailed upon to teach French until the French ambassador visited and my lamentable command of his language was humiliatingly exposed.

What moved me, though, is the school's continuing reverence for Jack, who died 22 years ago. He not only turned Mayo into one of India's leading schools, but also pioneered skiing in Kashmir and mountaineering in the Himalayas. He was awarded an Order of the British Empire by his own country and a Padma Shri, a top civilian honour, by India.

Mayo has named buildings and prizes after him and turned a room of the school museum into a veritable shrine containing his wooden skis, primitive climbing equipment, sporting medals, gramophone, suits and pipes.

Jack retired to a restored farmhouse on the edge of Ajmer where he grew sweet peas in his quintessentially English garden and played quoits in the courtyard each evening.

On Sunday mornings, I would go there to eat "unda rumble-tumble" - scrambled egg - cooked by his loyal servant Tanzuk. From his terrace, Jack enjoyed a bucolic view across hand-tilled fields to the ancient Aravalli hills, but it is all built over now.

In Jodhpur, I stay in the Umaid Bhawan palace (www.tajhotels.com/luxury/grand-palaces-and-iconic- hotels/umaid-bhawan-palace-jodhpur/overview.html), which was built largely as a famine relief measure in the 1930s.

Bapji inherited it at the age of four, when his father died in a plane crash. In a letter home, Jack wrote that it was a "white - or rather pink for it is of the local red sandstone - elephant". He reckoned without tourism.

Bapji has turned the palace into a sumptuous hotel where a drummer and bugler herald your arrival and servants bow and scrape as you process through the magnificent rotundas, halls and courtyards. No viceroy was ever so pampered.

From Jodhpur, I push deeper into rural Rajasthan, which is still a visual feast. Fields of vivid green wheat set off the arid brown hills. Colourful flags fly over whitewashed temples. Boys tend herds of goats and woman walk elegantly along dusty tracks, balancing water pots or bundles of firewood on their heads.

Late one afternoon, I take a train up into the hills on a British-built line that still has manually operated points and signals. It goes so slowly that monkeys run alongside, hoping for food. I sit in the open doorway of the ancient carriage as the sinking sun gilds the pastoral scenery, marvelling at its timeless serenity and briefly convince myself that nothing had changed.

But it has. Gone are the camel carts, the bullocks hauling water from wells in leaky leather bags, the laying of grain on the roads to get rid of the chaff.

The younger men no longer wear baggy cotton dhoti and lungi or the women such brightly coloured sari. Kunds - magnificent deep stone water tanks shaped like inverted pyramids - have been replaced by tube wells. Chai is sold in paper cups, not clay pots. The villages have electricity, televisions, mobile phones and Internet access, even ATMs.

The most startling transformation has been that of the crumbling forts I used to visit - Rohit, Sardargarh, Deogarh - where I remember three young child brides coming to seek the blessing of my host, Nahar Singh, the local Rawat (prince), while we were having lunch in a courtyard.

They are now "heritage hotels". I am prepared to dislike them, to dismiss them as Disneyfied cocoons for wealthy foreigners, but they have been beautifully renovated and brought much-needed employment to the villagers.

My last lingering reservations are banished when I return to Badnore, which I used to visit with Raghuraj Singh, the local Thakur (prince) and fellow teacher at Mayo. In 1961, Raghu's father had sold the imposing 16th-century fort to the government, which used it briefly as a teacher training college, then abandoned it.

Today, it is a ruin. The huge wooden entrance gates are disintegrating. The courtyards are overgrown. The walls and ceilings are collapsing.

"I feel very sad," says Raghu, now 82, who remembers when its stables were full of elephants and horses. "I don't think I will visit it again."

My last stop is in Udaipur and the magnificent Lake Palace hotel (www.tajhotels.com/luxury/grand-palaces-and-iconic-hotels/taj-lake-palace-udaipur/overview.html) with its gorgeous views across Lake Pichola to the soaring white flanks of the City Palace.

I used to visit the palace when I was a teacher. I had gone to meet the Maharani, wife of the Maharana. She was a beautiful young Englishwoman with a remarkable story.

Her name was Annabella Parker, a colonel's daughter from Gloucestershire. In 1964, she was backpacking around India, arrived at Mayo on Founder's Day and asked Jack how she could get to Udaipur. He pointed to the Maharana and said: "He'll take you."

The next thing Jack knew, they were married, to the fury of the Maharana's first wife, a Bikaner princess by whom he had had three children.

Annabella did her best to blend in. She wore a sari, covered her head and learnt Hindi. She championed animal welfare - a topic she would earnestly discuss while sitting in a palace chamber full of leopard skins and stuffed tigers. But neither the Maharana's Indian family nor the people of Udaipur ever accepted her. When the Maharana died in 1984, she was cast out and died in Britain.

None of this I learnt in Udaipur. I find no pictures of her, no mention in the palace museum. Those old enough to remember her will not speak for fear of offending the present Maharana. "Annabella has been written out of history," I am told.

My own romance with Rajasthan persists, but less intensely.

Like India, the state has made huge progress, but at a price. Its primary colours have dulled. There is less scope for real adventure.

As the poet A.E. Housman once wrote of nostalgia: "That is a land of lost content/I see it shining plain/ The happy highways where I went/And cannot come again."

• Martin Fletcher is a freelance writer.