The £1m-a-year drugs trade at Wandsworth Prison is being fuelled by corrupt staff, a report into the jail said.

Prison officers said the problem stems from hundreds of non-uniformed workers who have access to prisoners, and no prison officer had been dismissed because of drug trafficking in the last three years.

The annual Independent Monitoring Board report into Wandsworth - Europe’s largest prison which currently holds 1,641 inmates - stated: “The current annual market for drugs in Wandsworth was recently estimated to be worth £1million... and drugs appear to be more widely available than at any time previously.

It said: “There are concerns that a small number of staff are responsible for bringing the lion’s share of drugs into the prison.“ Stewart McLaughlin, secretary of Wandsworth Prison Officers’ Association - which represents 450 prison officers - said demands for access to prisoners meant keeping a check on access inmates’ was increasingly difficult, and prison officers were unjustly taking the flack.

He said: “Wandsworth Prison how has a huge number of staff, more than 700. About 300-350 are non-uniformed staff, community and social workers for example.

“We can’t monitor them all.”

He said prison officers were subject to spot checks, and worked regular shifts.

“The same checks are not taken on other prison workers,” he said, “and I cannot recall an officer being dismissed directly for drug trafficking in the last three years.”

The report added there were still serious problems with inmates using mobile phones to organise crime.

Some 307 mobile phones were seized from prisoners last year, including one which had images showing “the most graphic and violent images taken in another prison, including forced sex and stabbings”.

Chairman of the report David Jamieson said: “We have been raising the issue of jamming mobiles in prisons for the last five years and the Government has done absolutely nothing about it.

“It would solve a huge amount of problems if we could get rid of mobiles.”

Wandsworth Governor Ian Mulholland responded that technology to block mobile phone signals was being introduced into all UK prisons next year.