Standards in probation have worsened, leaving the public at risk, inspectors have found.

A review by HM's Inspectorate of Probation was commissioned after Dano Sonnex was jailed this summer for the murder of two French students while he was on probation.

The report, published today, found that only 54 per cent of cases in London met the level necessary to ensure the public are well protected. That was nine per cent below the score awarded when the inspectors reported on the service last year.

Today's report said many of the problems identified after Sonnex's conviction, which led to the resignation of David Scott, head of London probation, remained.

Chief inspector Andrew Bridges described the findings of the investigation into 276 cases in 10 London boroughs between April and July 2009 as "disappointing".

He praised staff for their efforts, but said there needed to be a "substantial improvement" in performance.

He said: "We have noted that there are a number of factors that have made it difficult for London staff to carry out effective practice.

"These included high numbers of particularly difficult offenders, some high individual caseloads - sometimes exacerbated by staff sickness - and an IT system that often froze or failed altogether" for days at a time.

In 18 cases criminals were rated at too low a risk, and only a quarter of high-risk offenders were visited at home after their sentence as required.

The inspectors' report comes one day before the Commons public accounts select committee publishes a report on the government's failed attempts to introduce a system that would unify the prison and probation services and replace a number of legacy systems currently being used.

They are now unlikely to be replaced as justice minister Jack Straw has announced that probation service funding will fall by 2.6 per cent, or £24m, in 2010/11.

Justice minister Maria Eagle said improved performance of the service in London was "a significant priority for ministers" and said "It is important to note the measures which have been put in place during and after the inspection period."

They include "prioritised training, new monthly targets, speedy recall processes and task forces for IT and HR", she said.