HONG KONG (REUTERS) - Among the hundreds of thousands of protesters who have clogged the streets of Hong Kong in recent weeks, silver-haired, bespectacled "Grandma Wong", usually seen waving a large British flag, stands out.

Ms Alexandra Wong, 63, who has smaller Union Jack flags pinned to her clothes and bags, has been on the front lines of mass protests in the former British colony and sometimes in tense stand-offs between police and student activists.

"I bought them in Shenzhen," a smiling Ms Wong, known affectionately as grandma, told Reuters of the flags, referring to the southern Chinese city across the border where she now lives.

"I had to ask secretly, because they only showed the Chinese flag. So I asked them if they had the British flag and they take it out to show me. If you don't ask, they don't show."

Ms Wong has joined millions in recent weeks who have taken to the streets to demonstrate against an extradition Bill that would allow people in Hong Kong to be sent for trial in mainland China, where human rights are not guaranteed.

Hong Kong returned to Chinese rule in 1997 with the guarantee of freedoms not enjoyed on the mainland, including an independent judiciary and right to protest, for at least 50 years.

Grandma Wong has been one of the few demonstrators over 30 to stay sometimes into the early hours to show her support for thousands of activists, many of whom joined 79 days of "Umbrella" protests in 2014 pushing unsuccessfully for full democracy for one of the most densely populated cities on earth.

"I stand with Hong Kong's future. I worry about Hong Kong youth," she said.

Some protesters have taken to waving the Union Jack during recent protests, certain to rile the authorities in Beijing, and a colonial-era flag, including the Union Jack, was unfurled when protesters stormed into the legislature on Monday night (July 1).

"I miss colonial times. The British colonial time was so good for us. I saw the future," Ms Wong said.

Ms Wong grew up in Sham Shui Po, one of Hong Kong's poorest areas, but was forced to flee to Shenzhen 13 years ago when she could no longer afford to live in one of the world's most expensive housing markets.

"I don't like to live there, of course. It makes me sad all the time, but I cannot live in Hong Kong," said Ms Wong, whose commute back and forth for protests can sometimes take five hours and costs her more than HK$100 (S$17.39).

The activist wears T-shirts in support of Hong Kong democracy when she travels into the city, but changes back into plain clothes when she returns home, so as not to draw scrutiny.

"I have no kids. That's why I am not scared at all," she said. "I don't have any worries about anyone. I just care about the future of Hong Kong youth."

Britain told China to honour its commitments to protect freedoms in Hong Kong on Tuesday. China has said Hong Kong is no longer any of Britain's business.