Liberal Democrat mayoral candidate Brian Paddick has urged judges not to overlook mandatory five-year sentences for possession of a firearm.
The call comes as new research by the Liberal Democrats reveals the number of guns seized at UK borders has more than halved in a year.
According to the party's research, up to nine times as many customs officers work on stopping cigarette smuggling than on gun smuggling.
Mr Paddick, whose main pitch is that he knows how to make Londoner feel safe, argued it was vital to stand firm on stronger sentences.
He said: "Letting offenders off the supposedly mandatory five-year sentence is sending out the wrong message. We need a real deterrent and judges should get on board to make sure that the sentences do exactly what they say on the tin."
If elected to take charge of London, Paddick has pledged to cut crime in London by 5 per cent every year during his first term.
He has also promised to not stand again for Mayor should he fail to reach his target of cutting crime after four years.
Paddick, along with his rival candidates Ken Livingstone and Boris Johnson, has been addressing the capital's Polish population to canvass migrants votes, according to the Federation of Poles in Great Britain.
Boris Johnson addressed a meeting of Poles while Mr Livingstone and Paddick have sent video messages.
As many as 65,000 recent migrants from Poland will be eligible to vote in the election on May 1.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article