Ms Evans and Mr Haw joined carol singers

About 100 singers tested the limits of the new Serious Organised Crime and Police Act by singing in Parliament Square on Wednesday evening.

The law bans demonstrating without police permission within a half-mile "exclusion zone".

No singers were arrested. Police said they treated it as a carol service, not a demonstration.

Singers included peace campaigner Maya Evans, 25, who was the first protester to be convicted under the act, after reading out the names of soldiers killed in Iraq at the Cenotaph.

This is a very good way of testing exactly how far we can push this law Maya Evans

She had feared being arrested again on Wednesday, as she would have been in breach of her conditional discharge, but no police officers turned up to the carol service.

"I was concerned but obviously I'm very strong in my conviction that this act is unjust, and I'm willing to take that risk," she said.

"This is a very good way of testing exactly how far we can push this law".

The law was prompted by anti-war protester Brian Haw's four-year peace vigil outside Parliament.

But ironically Mr Haw is the one protester exempt from the ban, due to a Home Office drafting error.

We treated the event as a carol service and not as a demonstration Metropolitan Police

He successfully argued in the High Court that as his protest pre-dated the law, he did not have to apply for authorisation to continue.

Since the law came into force in August, several people have been arrested and other protesters have been warned off.

Human rights lawyer Michael Schwartz, who was among the singers, said the new law was vague - as demonstrated by the lack of police officers on Wednesday.

"Is it compatible with human rights law, which is supposed to protect freedom of expression and assembly, particularly around Parliament, which is supposed to be the mother of democracy?," he added.