Davinder Singh, 31, was convicted of a sexual offence against a 15-year-old girl in February 2007 by Falkirk Sheriff Court.

Singh was fined and placed on the sex offenders’ register but has now failed to comply with the necessary registration requirements and it is thought he may have gone to England, it emerged yesterday.

Last seen in Falkirk on July 7 last year, Singh had been living in Central Scotland since February 2006.

He has been reported missing and a warrant has been issued for his arrest.

Central Scotland Police urged anyone who sees him or who knows where he may be to get in touch.

Singh is slim, 5ft 7in, black hair, brown eyes and of Indian appearance.

The Scottish Tories yesterday raised concerns that it had taken so long for Singh’s disappearance to come to light. It has been calling for tougher action to stop sex offenders slipping through the net.

The party’s community safety spokesman, John Lamont, said: “There are serious questions to ask here. Why are we only just learning about this man now, when he has been on the run for six months?

“Merely placing somebody on the sex offenders’ register is not enough. That is why Scottish Conservatives have repeatedly called for lie detector tests for sex offenders, as part of a package of measures which also include the naming and shaming of absconded sex offenders and GPS tracking.

“Here an absconded sex offender has not been named until now and that is unacceptable.”

Mr MacAskill has been under pressure to crack down on convicted sex offenders since Scotland’s worst paedophiles were jailed for life in October, last year.

Neil Strachan, 41, and James Rennie, 38, both from Edinburgh, were jailed in October for a catalogue of child pornography and abuse offences, which included the sexual assault of a three-month-old baby.

Strachan was already on the sex offenders’ register for previous offences.

In July, last year, Paul Hunter Redpath, 37, from Stranraer, described as a high-risk sex offender went on the run in Northern Ireland. Redpath, who was known to abuse alcohol and pose a serious risk to vulnerable children and young people

previously went missing in 2006 but was discovered in the Irish Republic.

A Scottish Government spokesperson said: “The vast majority of sex offenders comply with their conditions but where one seeks to evade the notification regime their details can be published through a range of media, including mass-circulation press and news websites.

“It’s widely recognised that each decision is an operational matter for police and local agencies, based on specific intelligence and a professional assessment of risk and the potential results of publishing or not publishing.

“However, the Justice Secretary has made clear his view that where a high risk sex offender goes ‘missing’ all options must be considered, including publishing details in mainstream media – just as has happened in several cases over the last year.”

Willie Manson, national co-ordinator of Multi Agency Public Protection Arrangements (Mappa), insisted all agencies were working “increasingly effectively” to identify and minimise risks posed by convicted sex offenders and protect the public.

Figures released in October, last year reveal more than 40 sex offenders were charged with another sexual or violent crime last year, an increase from nine the previous year.