The proposals would create a specific criminal offence of conspiracy to cause a forced marriage. At present prosecutors have to rely on proving offences such as kidnap, assault and false imprisonment against parents and relatives of victims.

Senior officers believe that nearly 500 forced marriages have taken place in London in the past two years while the national figure is believed to be much higher. Police lobbied the Government earlier in the year for precisely such a change.

There is concern among some women’s groups and others working to help victims of forced marriage that a criminal offence could deter women from coming forward. One said: “The chief concern among many of these women when they seek help is that their parents and families are not going to get into any trouble. If they think that their families will be prosecuted, they will be even more reluctant than now to speak.”

A Home Office spokesman confirmed that a consultation paper would be launched in late spring on whether a specific criminal offence should be created. There would be widespread discussion, he said, with victims of forced marriage, women’s groups and others “to see how best the law can be used to support victims”.

Police believe that an offence would also help to curb the incidence of so-called “honour killings”, as well as the incidence of abduction, assault, domestic violence and rape associated with forced marriage.

Honour killings are concentrated in the Indian, Pakistani and Bangladeshi communities but cases are also emerging involving women from Arabic and eastern European backgrounds.

Commander Andy Baker, who announced a police initiative this month on curbing “honour-based violence”, said that officers sometimes found it difficult to get enough evidence if plans for a forced marriage were in the early stages. An offence of conspiracy might allow police to use evidence that a forced marriage was being prepared by, for example, showing that plans were being made to take the victim abroad.

Police have begun taking a closer look at suspected honour killings since the murder in 2002 of Heshu Yones, a 16-year-old Kurdish girl killed by her father in West London. Mr Baker said that the number of honour killings had dropped from twelve in 2002 to one last year. But police are re-examining 109 murders between 1993 and 2003 which have been identified as suspected honour killings for clues about how to prevent future deaths. Cases include one from Sweden, which is co-operating in the research.

“Multiculturalism does not mean accepting the unacceptable,” said Sir Ian Blair, the Commissioner of the Metropolitan Police.

Victims are killed by their families for bringing “shame” on them, either for refusing to enter an arranged marriage or for having a relationship outside the community. Others are driven to suicide.

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