Tough prison sentences such as four years for trying to organize a riot via Facebook have triggered alarm in Britain that the government's crackdown over last week's unrest may be too harsh.

Britain's Conservative Party, which leads a coalition government, has promised tough action following four nights of violence in London and other cities to mend what it has described as Britain's broken society.

Civil liberties groups, legal experts and some politicians however say that disproportionate sentencing could only fuel a sense of injustice.

There's no doubt that in certain circumstances a firm sentence is required, said John Cooper, a senior crime and civil liberties barrister.

What concerns me is that the whole range of the sentencing process has been unduly and disproportionately cranked up ... influenced implicitly or explicitly by public opinion.

Many people in Britain are outraged over last week's rioting and looting that caused widespread damage and was linked to the deaths of at least four people.

Some agree with harsh sentencing, but worry they have been imposed under political pressure.

You should judge every individual case on its merits and every person on the basis of what they've actually done, rather than this creep toward .... judicial activism, where politicians put undue influence on the judiciary, said Daniel Hamilton, director of Big Brother Watch, which campaigns for civil liberties.

DISPROPORTIONATE PUNISHMENTS

In London, more than 1,000 people have been charged with crimes connected to the riots, which also spread to the cities of Liverpool, Manchester, Birmingham and Bristol.

On Wednesday, media reported that a young man had been given a four-year jail term for setting up a page on social networking site Facebook calling on people to riot in his home town.

Another young man received the same sentence elsewhere in England for a similar offence.

No riots broke out in the areas the men came from, and one media report said one of the young men had woken with a hangover the next day, deleted the web page and apologized.

It's very tempting for everybody to get carried away with the rhetoric and saying we should round up these monsters and deal with them draconically. What you're going to get if you start sentencing disproportionately is all sorts of anomalies, said Roger Smith, director of law reform group Justice.

He compared the young men's four-year prison term to a likely two years for breaking someone's leg in an assault.

Media outlets reported than one man had been jailed for six months for stealing bottled water worth 3.5 pounds ($5.78) from a supermarket looted during the riots.

Britain's Criminal Bar Association said that while it would be wrong to punish all crimes harshly because they were committed during the riots, judges and magistrates should be allowed to give higher sentences for a crime depending on the context in which it was committed.

Judges are entitled to conclude that these crimes have a number of aggravating features, born from the circumstances of the case, which mean that the sentences can and should be higher, the body's Vice Chairman Max Hill said in a statement.

But others argue that harsh sentencing for less serious crimes devalues punishments for more serious offences.

The Conservatives have defended the harsh sentencing, saying the sentences should act as a deterrent to others.

What happened on our streets was absolutely appalling behavior and to send a very clear message that it's wrong and it won't be tolerated is what our criminal justice system should be doing, Prime Minister David Cameron said.

But even his coalition partners the Liberal Democrats are distancing themselves from his approach. For less serious crimes, they advocate punishments such as helping to repair riot damage and being forced to meet victims of the disorder.

Short prison sentences for relatively petty offences go against the Ministry of Justice's own evidence that shows that short prison sentences are very ineffective at reducing reoffending, said Tom Brake, co-chair of the party's committee on home affairs, justice and equalities.

Other critics say also say the zero tolerance approach could be self defeating, given that Britain's prisons are already overflowing at a time of strained public finances.

We have doubled our prison population since the mid-1990s and seen tougher and tougher measures introduced each year, with an abundance of criminal justice legislation. Yet despite all this, the outcome of being 'tough on crime' was some of the worst street disturbances seen in decades, said Andrew Neilson of the Howard League of Penal Reform.

(Additional reporting by Stephen Addison; Editing by Maria Golovnina)