Prison officers at HMP Wandsworth, which houses murderers and rapists, are “scared to do their job” because of the threat of suspension, a union has said.

Staff safety was being compromised because of inspectors’ demands to stop restraining prisoners, Wandsworth Prison Officers’ Association (POA) said, adding authorities’ reluctance to punish inmates was fuelling the prison’s £1m drug trade.

The Prison Service (PS) said it was right to investigate claims of excessive force. However, the union claims come as figures obtained by the Wandsworth Guardian show the number of phones being smuggled into Europe’s largest prison appeared to be getting worse, fuelling fears that criminality was being organised from cells.

Prison security was reviewed in May when two gunmen killed 20-year-old Darcy Austin Bruce outside the prison shortly after he visited an inmate. Last November an independent monitoring board (IMB) report said the drug trade in the prison was worth £1m a year.

A POA spokesman said management was trying to reduce the number of times staff used control and restraint (C&R) techniques to address criticism from prison inspectors.

C&R is used to restrain inmates in aggressive situations and was an essential part of managing prisoners, the spokesman said. Prison officers using the technique were being “aggressively” investigated, he claimed.

The spokesman added: “It’s only a matter of time before an officer is injured unnecessarily because they are hesitant in using C&R. Staff are becoming afraid of doing their job. There’s always the concern they will be aggressively investigated by management.”

The spokesman added officers were asked to diffuse situations using other methods, but management was blind to the causes of potential trouble, like overcrowding and drugs.

“Management are asking us to reduce the number of fire extinguishers when they should be asking us to reduce the number of fires,” he said. “But they haven’t given us anything to replace C&R with.”

He added the views were backed up by evidence.

“In one incident an officer who was alleged to have used excessive C&R was suspended for months,” he added. “They have since returned to work, after being disciplined, but are hesitant to use C&R where necessary again.”

A PS spokesman said use of force should only be used when all other strategies have been “deemed unsuccessful”. He said: “It is right and proper that alleged use of excessive force by prison staff is fully investigated.”

November’s IMB report also highlighted the prison’s drug problem. It said: “Phones are used to drive the drugs trade in Wandsworth . . . drugs appear to be more widely available than at any time previously.”

It added: “We have seen a phone seized by security which had the most graphic and violent images taken in another prison, including forced sex and stabbings.”

But, despite the phone problem being highlighted for years, figures gained under the Freedom of Information Act showed the number of mobile phones confiscated from inmates had risen.

In 2007, 307 phones were confiscated from inmates and in 2008 the figure had risen to 382.

In addition 215 “drugs and unknown substances” were confiscated along with 119 phone sim cards and 142 phone chargers and leads.

The PS spokesman said it had introduced body scanning chairs to combat the problem and drug misuse in prisons, as measured by the random mandatory drug testing programme, had declined by 63 per cent since 1997.

He added the law had been strengthened so anyone convicted of bringing a mobile phone or components to prison now faces up to two years in jail.

But – according to the POA spokesman - even when prisoners were found with phones authorities did little to deter them.

He said one inmate who was caught with a mobile phone, sim card and charger in his cell three times within three months, but was given little more than a slap on the wrist.

The spokesman added: “For the first offence he was caught with a phone and got a loss of privileges and 21 days of no association [not allowed time with inmates]. The second time, again with a phone, he got 16 days added to his sentence and 14 days of no association.

“On the third occasion he was caught with a mobile phone, sim card and charger and seven days cellular confinement, suspended.

“The officer who caught him said they wouldn’t bother again. What is the motivation for a prison worker to risk attack when nothing gets done about it?”

In contrast, he said, one prison officer was suspended for 13 months, on full pay, on corruption charges. He said: "The whole case cost about £100,000 and the charge was dropped.”

A report last week said Wandsworth Prison was operating at 150 per cent capacity, currently housing 1,650 inmates despite its official capacity of 1,107.