Parliament's human rights watchdog has raised "significant concerns" over possible use of new powers to strip naturalised Britons of their citizenship and leave them stateless.
As the Government's centrepiece Immigration Bill enters committee stage in the House of Lords, the Joint Committee on Human Rights (JCHR) said it fears the main purpose of the power to deprive citizenship is to target naturalised Britons while they are abroad.
The group of MPs and peers said the clause in the immigration bill would risk breaching the UK's international obligations to the state which admitted the British citizen to its territory.
Committee chair Dr Hywel Francis MP said: " The UK has historically been a champion of efforts to reduce statelessness throughout the world and it is disappointing to see this position shift in such a dramatic way.
"The new power will lead to an increase in the number of stateless people and exposes British citizens to the risk of being left stateless.
"As the Supreme Court recently said, statelessness is an 'evil' - it takes away the right to have rights.
"The power does not in itself put the UK in breach of any of its international obligations in relation to statelessness but it does pose the risk of breaching our international obligations to other states.
"We are particularly concerned about the power being used when citizens are abroad.
"Parliament needs more information about how similar powers have been used in the recent past and assurances about how this power will be used in the future."
The committee has recommended that the Immigration Bill is amended to introduce a precondition of making an order by which revoking citizenship is compatible with UK obligations under international law.
And the group of MPs and peers warned that the power will lead to an increase in statelessness, even though it accepts that the change does not in strict legal terms involve any breach by the UK obligations under the UN Conventions on Statelessness.
The committee also criticised the Government for refusing t o reveal to Parliament the number of cases in which the power to deprive citizenship has been exercised while the UK citizen is abroad.
Home Secretary Theresa May tabled an amendment to the Bill in January to allow the removal of a UK passport from any person whose conduct is deemed "seriously prejudicial to the vital interests of the UK".
The Home Secretary already had power to take away British citizenship from tho se with dual nationality; however, this change would allow her to make people stateless if they have been naturalised as a British citizen.
Human rights campaigners branded the move an "alarming development", giving the Home Secretary power to "tear up people's passports without any need for the kind of due process".