PRESSURE is mounting on the British Government to grant full nationality to Hong Kong's ethnic minorities. The tension is increasing because of the success in the House of Lords of proposed legislation to offer the group British passports. The Lords approved a formal second reading of the backbench bill, proposed by Liberal Democrat peer Lord Bonham-Carter, designed to ensure that the 7,000-strong ethnic minority community does not become stateless in 1997. But the success of the legislation so far does not mean it will be accepted later in the Commons where it is almost guaranteed to fail. Instead, it will only add to the potential embarrassment for the British Government. The Government was defeated in July when peers backed a similar demand in a debate - but with no legal force on ministers. Since then, Governor Chris Patten has raised the issue with the Home Secretary Michael Howard - only to be rebuffed. Pleading the case of the ethnic minority community in the territory, Lord Bonham-Carter, said: ''This is a unique case. What is taking place in Hong Kong is without precedent. Hong Kong is not being offered independence, but is being transferred to another state where these British nationals will have no right to become citizens. ''The purpose of the bill has the support of two former governors of Hong Kong, the present Governor, the unanimous support of Legco, Justice, the International Commission of Jurists and the Commonwealth Human Rights Commission. Only the Home Office appear to oppose it.'' Former governor Lord Wilson of Tillyorn declared his and former governor Lord MacLehose's support for the bill. ''These are real people with real problems, to whom we have real obligations,'' he said. After the third generation they would have no option but that of Chinese citizenship, he warned. ''It is rather like generation after generation climbing up a ladder, the rungs of which get weaker and weaker and the ladder eventually gives out.'' He urged the Government to back the bill and improve its drafting in what was a complex area of legislation. ''I believe the ball is being kicked in the right direction,'' he said. ''I would like to see the Government pick it up and run with it themselves, but above all, I would like to see it get beyond the touchline.'' But Home Office minister Earl Ferrers said the Government believed the bill was unnecessary and undesirable. He claimed the ethnic minorities were already adequately protected, that they had no wish to come to Britain and that the UK was very likely to accept them if they were ever forced out of China. He accused Lord Bonham-Carter of ''riding a hobby horse'' and told peers it would be ''inappropriate'' to change the existing arrangements. He claimed that most of the ethnic minority community had either British nationality and either Indian or Pakistani citizenship and denied they would become stateless after 1997. They would continue to have a right of abode in Hong Kong after 1997 even if they did not have one elsewhere. China had said the minorities were welcome to remain in Hong Kong and that they could apply for Chinese citizenship after 1997. Mr Ferrers said: ''There is no reason to suggest that a change of sovereignty should threaten this particular group and that they should therefore be given special treatment in the form of a right of abode not in Hong Kong but in the UK.''