Human rights groups have opposed a plan by police chiefs to make flag-burning by protesters a new criminal offence.
The Danish flag was burnt in the cartoon row protests
The Liberal Democrats and Liberty said new legislation was unnecessary because police had powers to tackle incitement.
Scotland Yard has drawn up proposals to submit to the Attorney General because of a belief the UK has become a soft touch in dealing with extremists.
The plans, backed by Labour MP Shahid Malik, would also ban protesters from hiding their faces from police.
But that would not include Muslim women wearing a veil.
Shami Chakrabarti, Liberty's director, said: "We will have to look at the detail of these proposals but the police already have wide powers, especially for dealing with people wearing masks.
"I wonder how hard-working officers on the beat today will feel knowing their senior officers are spending so much time dreaming up unnecessary legislation."
Criminalising flag-burning would be an unacceptable restriction of freedom of expression, said Liberal Democrat MP Evan Harris, a member of the parliamentary Joint Committee on Human Rights.
"The battle against terrorism and extremism is not a matter of yet more public order offences and it is vital that we preserve free speech where no crime is incited," he said.
The plans have been drawn up by Scotland Yard and submitted to the Attorney General Lord Goldsmith, by Britain's most senior Muslim police chief, Assistant Commissioner Tarique Ghaffur.
Mr Ghaffur, responsible for public order in the capital, said he was concerned the UK had come to be seen at home and abroad as soft on extremist demonstrators.
He said police wanted "a change in the law on the burning of flags - to make that illegal".
Mr Malik, MP for Dewsbury, said burning a flag was clearly an incitement to violence practised by a small number of "thugs" who get to the front of demonstrations.
"They hijack what are very legitimate and peaceful protests.
"Not only do they spoil it, but they have the potential to turn it into something much more sinister."
But Massoud Shedjareh, of the Islamic Human Rights' Commission, said whether it was incitement or not depended on the circumstances, but police already had powers to deal with it.
A Home Office spokeswoman said she was unaware police thought existing powers were inadequate but ministers were ready to listen to any suggestions from officers.