How long is he looking at in prison?

HM REVENUE AND CUSTOMS are helding my friend for 拢4 million pound , they are going to arrest him tommorrow.

he is the director of some company called dorval limited in wolverhampton, he became the director of the company on 9/9/07

the 4 billion tax hasnt been paid since sept 2005 so why is my friend being liable

what are the possible rights that he may have to deal with this situation.

the owner of dorval limited whom actually hasnt been paying for the tax has ran off to india with his son,

so help

As a director of the company he is an officer of the company and therefore can be held liable for the company's actions. The fact that the company has not paid the tax bill is the responsibly of the business - however he will not be arrested for this. A tax bill doesn't cause anyone to be arrested - it's more likely that the company hid it's tax liabilty and the directors are being pursued for fraud - but it depends whether not they have co-operated with HMRC during the enquiry or if they have denied all wrong-doing.
Only your 'friend' can tell you the situation - HMRC will have full advised him of his position. Any sentence will be determined by the courts.

Personally I dont know, but often a very quick 5 minute call to a solicitor for free will help you out over the phone.

Good luck - fingers crossed!
It may just be a preliminary thing...