An unexplained “dramatic” rise in rape and sexual offences across Sutton has caused serious concern among women’s groups.

The percentage increase in rapes, up by 50 per cent compared to last year, is the third highest in the whole of London.

Ruth Hall from Women Against Rape described the rise as “startling” and demanded an explanation from police.

The number of reported rapes rose from 28 in 2006-2007, to 42 by September this year, a 50 per cent increase. Sexual offences, which include indecent assault and underage sex, rose from 107 in 2006-07 to 161 in the 12 months to September 2008, a 50.5 per cent leap.

Across London, Metropolitan Police figures showed an increase of just 13.3 per cent for rape and 2.4 per cent for sexual offences.

The Met’s figures show that only the boroughs of Croydon and Hillingdon reported a larger percentage rise in rapes this year.

Miss Hall said: “Although we acknowledge there are some police out there who want to get convictions, some are still making appalling mistakes when dealing with rape victims.”

Pete Smythe, chairman of the Metropolitan Police Federation said: “It is a fairly dramatic rise. Reporting of rape has changed and I would like to think women are more confident in coming forward and reporting incidents.

Angie Conroy from Rape Crisis England said: “A 50 per cent rise is very concerning, I don’t think that it can be put down to women being more confident in reporting.

“Something needs to be done.”

“I am not aware of Sutton police encouraging women to come forward any differently to the rest of the Met.”

Councillor Paul Scully, leader of the Conservative group on Sutton Council, said: “The 50 per cent increases are a cause for deep concern. I shall be writing to Chief Superintendent Bob Reed to express my concern and find out why there has been a significant spike in these offences from baseline figures.”

A spokesman for Sutton police said: “We regard all reports of sexual offences as serious and we investigate all such crimes in a robust and thorough manner, while dealing with victims and witnesses in a sensitive and supportive way.

“We actively encourage victims to come forward. We have a specialist investigative team – Sapphire – dedicated to investigating all sexual offences.

“They have been working with victims more closely than ever to build their confidence and to encourage them to come forward with the information we need to prosecute offenders in court.

“Sutton is one of the safest London boroughs for all types of crime, including sexual offences.”