One in five adults caught holding a gun illegally does not serve a prison sentence, according to Government figures.
Forty five people aged 18 and over out of 248 (18 per cent) found with a firearm were not sent straight to prison.
Meanwhile one in three adults convicted of gun possession escaped the "compulsory" minimum sentence of five years in prison.
Only 132 of the 208 adults (64 per cent) aged 21 and over sentenced for possession of a firearm were given a "mandatory" five year sentence.
But the average amount of time spent in prison by those found with guns increased slightly to 56 months.
Meanwhile four out of 10 young adults (aged 18 to 21) escaped the minimum three year jail term, as did almost nine out of 10 children.
The figures related to 2007, the last year for which they were available, were revealed in answer to a Parliamentary question tabled by the Liberal Democrats.
They show judges have been using their discretion to impose a more lenient sentence in exceptional circumstances.
The five-year mandatory minimum for adults caught with an illegal gun was introduced by the Home Office in England and Wales in 2004.
In a recent case, a judge criticised the legal minimum sentences for firearms offences after hearing of a tragic family case.
Music teacher Guy Button, 30, admitted handing a pistol to his terminally ill father so he could shoot himself dead at Northampton General Hospital last October.
Judge Richard Bray said the case was "very sad" because legislation gave him little discretion to hand down a shorter jail term or alternative sentence.
Liberal Democrat home affairs spokesman Chris Huhne said: "Ministers are playing Mr Macho on minimum sentencing, but this is just posturing is just empty words.
"One in five adults caught with a gun avoids prison, making a mockery of the supposedly 'mandatory' five year tariffs.
"Judges are right to take account of circumstances when it comes to sentencing. That is what they are there for. If we remove their discretion, we may as well put a computer in court instead.
"The recent comments by Judge Richard Bray in the case of Guy Button, who provided his father with a gun to kill himself, demonstrate what the judiciary think of this law.
"The way to cut gun crime is to catch more criminals with better policing, as the sentences are already tough enough.
"Mandatory sentences undermine the expertise and independence of judges and as these figures show are all too easily ignored.
"There are also serious concerns that mandatory sentences deter people from handing themselves in and co-operating with the police."Reuse content