Two men who posted messages on Facebook inciting other people to riot in their home towns have both been sentenced to four years in prison by a judge at Chester crown court.

Jordan Blackshaw, 20, set up an "event" called Smash Down in Northwich Town for the night of 8 August on the social networking site but no one apart from the police, who were monitoring the page, turned up at the pre-arranged meeting point outside a McDonalds restaurant. Blackshaw was promptly arrested.

Perry Sutcliffe-Keenan, 22, of Latchford, Warrington, used his Facebook account in the early hours of 9 August to design a web page entitled The Warrington Riots. The court was told it caused a wave of panic in the town. When he woke up the following morning with a hangover, he removed the page and apologised, saying it had been a joke. His message was distributed to 400 Facebook contacts, but no rioting broke out as a result.

Sentencing Blackshaw to four years in a young offenders institution, Judge Elgan Edwards QC said he had committed an "evil act". He said: "This happened at a time when collective insanity gripped the nation. Your conduct was quite disgraceful and the title of the message you posted on Facebook chills the blood.

"You sought to take advantage of crime elsewhere and transpose it to the peaceful streets of Northwich. The idea revolted many right thinking members of society. No one actually turned up due to the prompt and efficient actions of police in using modern policing."

Sutcliffe-Keenan, the judge said, "caused a very real panic" and "put a very considerable strain on police resources in Warrington". He praised Cheshire police for their "modern and clever policy" of infiltrating the website.

The Crown Prosecution Service said in a statement that the men's posts on Facebook "caused significant panic and revulsion in local communities as rumours of anticipated violence spread".

It added: "We were able to serve upon the defence in both cases sufficient case material that led to early guilty pleas and we were able to present the facts in both cases in a fair but robust manner.

"While the judge heard the two defendants were previously of good character, they admitted committing very serious offences that carry a maximum sentence of 10 years. The consequence of their actions could have led to more disorder and this was taken into account."

The heavy sentences came as defence lawyers and civil rights groups have criticised the "disproportionate" sentences imposed on some convicted rioters as the latest official figures show nearly 1,300 suspects have been brought before the courts.

The revelation that magistrates were advised by justices' clerks to disregard normal sentencing guidelines when dealing with riot-related cases alarmed a number of lawyers who warn it will trigger a spate of appeals.

Also on Tuesday, a looter was warned he could be jailed for helping himself to an ice-cream cone during disturbances.

Anderson Fernandes, 22, appeared before magistrates in Manchester charged with burglary after he took two scoops of coffee ice-cream and a cone from Patisserie Valerie in the city centre. He gave the cone away because he didn't like the flavour.

Fernandes admitted burglary in relation to the ice-cream and an unconnected charge of handling stolen goods after a vacuum cleaner was recovered from his home. District judge Jonathan Taaffe said: "I have a public duty to deal swiftly and harshly with matters of this nature." Fernandes will be sentenced next week.

In sentencing four other convicted Manchester rioters, a crown court judge, Andrew Gilbert QC, made clear why he was disregarding sentencing guidelines when he said "the offences of the night of 9 August ... takes them completely outside the usual context of criminality".

He added: "The principal purpose is that the courts should show that outbursts of criminal behaviour like this will be and must be met with sentences longer than they would be if the offences had been committed in isolation. For those reasons, I consider that the sentencing guidelines for specific offences are of much less weight in the context of the current case, and can properly be departed from."

The Ministry of Justice's latest estimate, at midday on Tuesday, shows the courts have dealt with 1,277 alleged offenders of whom more than 700 have been remanded in custody. Two-thirds of the cases were in London.

By midday on Monday, 115 people had been convicted; more than three-quarters of those were adults. About 21% of those appearing before the courts have been juveniles. The proportion of alleged youth offenders was higher in Nottingham, Birmingham and Manchester. An MoJ spokesperson said: "Everyone involved with the courts and prison service has put in a huge effort to make that possible and that work will continue."

But doubts are now being expressed about the fairness of some sentences. For example, one student has been jailed for six months for stealing a bottle of water from a supermarket.

Sally Ireland, policy director of the law reform organisation Justice, said: "The circumstances of public disorder should be treated as an aggravating factor and one would expect that to push up sentences by a degree, but not by as far as some of the cases we have seen.

"Some instances are completely out of all proportion. There will be a flurry of appeals although, by the time they have been heard, those sentences may already have been served.

" There's a question about this advice [from justices' clerks] and whether it should have been issued at all. We would expect them to be giving advice [to magistrates] in individual cases rather than following a general directive."

Rakesh Bhasin, a solicitor partner at the law firm Steel & Shamash, which represents some of those charged following the riots, said some reported sentences seemed to be "disproportionate".

Paul Mendelle QC, a former chairman of the Criminal Bar Association, said: "The idea that the rulebook goes out the window strikes me as inherently unjust. It sets all manner of alarm bells ringing. Guidelines are not tramlines. There are guidelines and they take account of aggravating and mitigating circumstances.

"There have been rulings following the Bradford riots and Israeli embassy demonstrations that said which sort of guidelines should be followed. I don't see why [magistrates] should be told to disregard these."

The judiciary and the MoJ have denied that they were involved in circulating the advice to justices' clerk last week.