Peers have called for the 650-year-old Treason Act to be updated to prosecute returning jihadists who have "betrayed" Britain.
Home Secretary Sajid Javid came under pressure at question time after deciding to revoke Islamic State bride Shamima Begum's British citizenship.
Labour former security and counter-terrorism minister Lord West of Spithead said it was "appropriate that as a nation we show how repugnant this is and how appalling that sort of behaviour is".
Lord West said that, as a minister, he found it difficult at times to take to court people who should have been prosecuted there.
"This seems to me a way it can be done," he added. "Update the treason law and show these people to be traitors, something that our nation really believes they are."
Home Office minister Baroness Williams of Trafford said recent legislation had already given more powers to the courts to prosecute.
"I agree the 1351 Treason Act is rather an old Act. Of course it was relatively recently updated in 1861."
Lady Williams said she was not dismissing the demand.
The Home Secretary had said he would look at it and the Home Office kept all laws under review.
But she said prosecuting terrorists for treason risked "giving their actions a political status or glamour they do not deserve, rather than treating them merely as criminals".
Independent crossbencher Lord Alton of Liverpool said no one wanted to glamorise such actions but those who sought to justify the murder of British citizens in the bombing of the Manchester Arena in 2017 or took up arms against British forces and civilians had "betrayed this country, its people, its values and its laws".