Tough sentences are being handed out to those involved in the riots to appease "angry Britain", lawyers and campaigners warned today.

The rush to send out a message in the wake of the riots and the desire to make an example of those involved is leading to "some very bad sentences" that risk clogging up the courts and prisons in England and Wales, they said.

But Prime Minister David Cameron insisted it was right for the courts to hand out tough sentences after two men who tried to incite riots on Facebook were jailed for four years - even though the riots they tried to plan never happened.

Mr Cameron said: "What happened on our streets was absolutely appalling behaviour and to send a very clear message that it's wrong and won't be tolerated is what the criminal justice system should be doing.

"They decided in that court to send a tough sentence, send a tough message and I think it's very good that courts are able to do that."

But leading criminal barrister John Cooper QC warned that some sentences were being handed down as a "knee-jerk reaction", "responding to the public's anger and the politicians' rhetoric".

"It's the duty, in my view, of all those who direct sentencing to be independent and not to be influenced by angry Britain," he said.

"There's no doubt that some individuals will need to be sentenced very firmly, but my concern is that the sentences given in the last week have been disproportionate and somewhat hysterical.

"What's happening here is they're being unduly increased to appease public anger and, as far as the magistrates are concerned, potentially influenced by the views of politicians."

Mr Cooper went on: "The divergence from normal sentencing procedure is also shown in bail.

"They're now in custody being paid for by the taxpayer when two weeks ago they would have been in the community with stringent conditions."

Two in three people charged in connection with the riots and looting have been remanded in custody, compared with a remand rate of just one in 10 for serious (indictable) offences in 2010, Ministry of Justice figures showed.