The Burmese ambassador, Dr Kyaw Win, was summoned to the Foreign Office to be told of the Government's grave concern over the treatment of the Britons, which it said was a breach of the Vienna Convention on human rights.
Rachel Goldwyn, 28, of Barnes, south-west London, is being held in custody after being arrested for singing a civil rights song at a demonstration in the Burmese capital, Rangoon. James Mawdsley, 26, from Cheshire, who was arrested last Thursday, has been jailed for 17 years for entering Burma illegally and carrying anti-government literature.
Ms Goldwyn's mother, Dr Charmian Goldwyn, and her husband, Ed, a television producer, went to the Burmese embassy in London yesterday to apply for visas to visit the country, but were told that their application would have to "go right to the top". They had not known that their daughter was in Burma.
Dr Goldwyn said: "I am really trying not to think about all the ghastly possibilities ...
"We in common with many others share and understand [Rachel's] hopes for democracy in Burma but ... by now she must realise that her efforts have been misapplied. If she could be returned we would do our best to get her to resume her career and use her idealism in a more constructive fashion without returning to Burma."
A Foreign Office spokesman said: "We need to know, among other matters, exactly what kind of legal advice and representation, if any, these two people got as well as the state of their health. We are very worried that we are not being allowed access."