Home Office minister Tony McNulty has warned against "nipping around the edges" of British values with measures taken to tackle the terror threat.
Glasgow Airport was the scene of an attempted attack
He told a security conference it was possible more could be done "with a degree more rigour within the law".
Ministers are consulting on a range of possible new terror laws but say they want consensus and will not be "rushed into" new laws after the car bombings.
The Tories and Lib Dems both say they welcome a more consultative approach.
Continuing the less strident tone since Gordon Brown succeeded Tony Blair as prime minister, Mr McNulty said: "How can we in the fullest sense seek to get everyone signed up to the broadest values of the UK, if we are nipping around the edges of the legitimacy of those values in our legal responses?"
Among options being looked at are toughening the control orders regime, which imposes restrictions on terror suspects in cases where there is not enough admissible evidence to bring a prosecution.
A number of terror suspects have absconded while under control orders.
The UK's reviewer of terror laws, Lord Carlile, said on Monday he thought that courts might now accept tougher restrictions under the orders in the light of the attempted car bombs.
And in his speech to a security conference on Tuesday, Mr McNulty said: "It may be that we haven't thought in rigorous enough terms on how we capture these individuals under the law.
"It may well be that we can do with a degree more rigour within the law and control orders are inappropriate.
"Until someone comes up with something more appropriate we are always going to have this twilight zone."
Ministers have always said control orders were "far from the best option" in dealing with cases of terror suspects where there was not enough evidence to bring a prosecution.
They were brought in after courts ruled against the previously used option of detaining terror suspects in prison indefinitely without charge.
The conference comes days after three failed car bombings - two in London and one in Glasgow - and a string of security alerts, which have seen the UK move to its highest level of terror alert - critical.
It is thought there are up to six doctors among the eight people arrested in connection with the attacks.
In an interview with BBC One's The Daily Politics, the Conservatives' new security spokeswoman Dame Pauline Neville-Jones said border security would have to be tightened.
"It's one of the things which is an absolute principle in all of this, you must have a tight perimeter," she said.
She also said Britain may have to consider the monitoring people coming to the UK from "sensitive countries" - by requiring them to keep immigration officials informed if they changed their address.
She said it would be impossible to monitor all foreign-born professionals, but checks could be done on records of those from certain countries.
"You don't follow them round, but given the threat we now face, it would be sensible to go back through the records of people here," she said.