Possession of all drugs for personal use should be decriminalised in order to tackle overcrowding in British prisons, the Liberal Democrats have urged.

Calling for a radical overhaul of sentencing in the UK, the party calls on the Government to end the custodial punishment of drug users “that pose no threat to society”.

Under current laws possession of Class A drugs, such as crack cocaine, cocaine, ecstasy and heroin, can result in up to seven years in prison, an unlimited fine or both. The length of the penalty depends on the drug amount an individual has in their possession.

Drugs falling into the Class B category, including cannabis and amphetamines, can result in five years in prison and an unlimited fine. Class C drugs can result in a custodial sentence of up two years.

But the Lib Dems, who have advocated decriminalising drugs in the past, believe removing prison sentences for personal possession will alleviate the strains on the UK’s prison system. Citing evidence from the House of Commons library the party claims there are more than 11,000 people imprisoned for drug related offences.

The party also called on Liz Truss, the Justice Secretary, to increase the number of prison officers beyond the 2,500 already promised. It comes as the party holds its spring conference in York, with leader Tim Farron expected to address the party faithful at a speech on Sunday.

In order to stem the growing prison population in Britain at the end of last year, senior cross-party politicians wrote to Ms Truss calling for the number of inmates to be reduced by 40,000 – almost a half – to levels seen under Margaret Thatcher’s premiership.

But the proposal from the Lib Dems comes after the latest figures from the Council of Europe claimed Britain had the largest prison population in Western Europe at 95,248.

Jonathan Marks, the party’s justice spokesperson, said the rise in prisoner numbers combined with a fall in the number of prison staff had created “unsafe environments where violence is widespread” and the “use of illegal drugs abounds”. Prisoners with mental health issues, he added, “slip though the cracks”.

Mr Marks continued: “The simple fact is we will never turn prisons into places of rehabilitation and reform unless we send far fewer people in jail. The Government has finally admitted that prisons must act as places of education and reform and the proposals in the Prisons and Courts Bill are largely welcome.