I think that the existing law does not properly distinguish between forced marriages and arranged marriages, i.e. it is regarded as a quaint cultural thing rather than an oppressive thing. But in cases of forced marriage, people are sometimes prosecuted for other related offences such as abduction, false imprisonment, blackmail, etc. (because anyone who is the subject of a forced marriage is almost certainly the victim of other crimes which go along with it). I agree with the implication in your question, i.e. that it should become a specific offence, so that it will be easier to prosecute cases.