The Coalition will not be forgiven if control orders imposing virtual house arrest on terror suspects are scrapped and there is another 7/7 style attack, the Government's independent reviewer of terrorism laws said.
Lord Carlile said he did not like the idea of the controversial orders, which include electronic tagging and home curfews, but insisted they are essential for security.
Speaking in The Sun, the Liberal Democrat peer, said: "Security and police chiefs have made clear the necessity for the orders. We ignore their advice literally at our peril."
In a direct challenge to the Government to keep the legislation, he added: "The courage to protect public safety surely will be recognised.
"The failure to do so will not be forgiven if some terrible terrorism event happens."
Lord Carlile said he agreed the orders need to be reformed but insisted the key restrictions must be kept.
A review of counter-terrorism legislation was due to report before Christmas but has been delayed until early 2011 because of ongoing negotiations between ministers.
Mr Clegg's Liberal Democrats fought the General Election on a manifesto commitment of abolishing control orders.
Introduced under the former Labour government, they have been strongly criticised by civil liberties campaigners but police and the security services have repeatedly stressed the need to be able to contain suspects they are not able to charge.
The review, also looking at the controversial 28 day pre-charge detention period for terror suspects, was announced by Home Secretary Theresa May in July.
It is being overseen by former director of public prosecutions and Lib Dem peer Lord Macdonald of River Glaven.