Magistrates have denied accusations from the president of the Prison Governors Association that there has been a "feeding frenzy" of disproportionate sentencing of those convicted in the aftermath of the recent riots.

Eoin McLennan-Murray claimed courts had shown "naked popularism" in their punishments and that it was probable some people were being treated unfairly. There had also been far more use of people being remanded in custody pending further hearing of their cases.

He first criticised the courts to the Independent on Sunday, saying: "It's like when you've got sharks and there's blood in the water and it's a feeding frenzy. There's a sentencing frenzy and we seem to have lost all sight of proportionality," McLennan-Murray said.

"It's appealing to the populist mentality, and that's not the best basis on which to sentence people. The norms of sentencing are being ignored."

Speaking on Radio 4's Today programme on Monday, McLennan-Murray said there had been a seven-fold increase in the use of remand. He said this was putting pressure on prison places, adding: "This kind of speedy, across-the-board justice probably means a number of people are dealt with unfairly."

But the chairman of the Magistrates' Association, John Thornhill, called the claims "unreasonable and unfounded" and said he was "angry and concerned" by the claims. He told Today it was "just not the case" that normal sentencing was being ignored.

"The sentencing guidelines are very clear. Let's remember that these are serious offences. In most cases people are charged with burglary and in some cases aggravated burglary," he said.

"In a very short period of time far more people - a seven-fold number - were arrested for seven-fold the amount of serious offences. So it would be expected we would have seven-fold sentencing."

He added that criticism of magistrates was "totally misdirected" because "the vast majority of sentences have been imposed by the professional judiciary, not by the lay magistrates".

The prison population in England and Wales reached a record high for the third consecutive week last Friday as courts continue to jail people involved in the riots. The total number of prisoners hit 86,821, after a further 167 people were jailed. The population is now only 1,500 short of the usable operational capacity.

The Prison Service has already warned there could be unrest in jails as convicted rioters and looters are imprisoned.

A Guardian analysis of 1,000 riot-related cases heard by magistrates found those already sentenced were receiving prison terms 25% longer than normal and a 70% overall rate of imprisonment which compared with a "normal" rate of just 2%.