About 120 police officers holding shields stood guard outside the British embassy and nearby Swiss embassy, as flag-waving protesters erected a steel barricade and blocked all traffic on a major road in the downtown area.
Supporters of the People's Alliance for Democracy (PAD), which is trying to bring down the elected government, carried banners of Thaksin and his wife Pojaman reading 'Wanted for crimes against the kingdom of Thailand.'
A police officer at the scene said around 300 protesters had turned up, and more were expected ahead of a planned march down Sukhumvit Road, a key tourist and business thoroughfare in the capital.
'Why doesn't England send Thaksin back to Thailand to be put in jail?' PAD spokesman Sarocha Pornudomsak shouted to the crowd.
'We are here to tell (British Prime Minister) Gordon Brown that England should not keep a bad guy in the country.'
Thaksin fled to Britain in August, two months before he was sentenced in absentia to two years in jail for conflict of interest after helping his wife buy state-owned land when he was Prime Minister.
He has claimed he would not get a fair trial in Thailand on the corruption charges that have mounted against him since his overthrow in a September 2006 coup.
Many of the PAD supporters outside the British embassy waved Thai flags, while others carried banners of current Prime Minister Somchai Wongsawat - Thaksin's brother-in-law - and the word 'Murderer'.
Mr Somchai has been under increasing pressure to step down since October 7, when police fired tear gas on PAD supporters who were trying to blockade parliament. Two people were killed and nearly 500 injured in the clashes.
The PAD launched its campaign to bring down the democratically elected government in May, saying it was running the country on behalf of Thaksin, whom they accuse of corruption and nepotism. -- AFP