One in seven inmates at Sussex prisons has failed a recent drugs test, Home Office figures show.

A total of 522 prisoners were tested for illegal substances at Lewes and Ford prisons in the ten months to January this year. Of those, 78 tested positive and 444 negative - a failure rate of 15 per cent. This was up slightly from the 13 per cent of inmates who tested positive in 2005-06.

Prison service targets state the drug test failure rate should have been kept below 10.3 per cent in 2006-07.

But Lewes Prison in East Sussex, where 43 out of 270 drug tests were positive last year, ended up with a 16 per cent failure rate - up from 9.5 per cent in 2005-06. At Ford Open Prison in Arundel, 35 out of 252 drug tests (13.8 per cent) were positive last year, down from 16.3 per cent in 2005-06.

William Higham, head of policy at the Prison Reform Trust said the latest figures proved drug taking was "endemic" in prisons in England and Wales.

He said: "There is a cast iron link between drugs and offending.

We know that drugs cost around five or six times more (in prison) than they cost in the community. This high cost means people will find a way of getting them into prison."

A Home Office spokesman said: "Drugs are sadly valuable currency in prison and those outside go to great lengths to get them in."