In at the deep ?

Been asked to look at the Accounts of a Deep Sea Diver to establish whether it would be of benefit to Incorporate his existing Sole Trade business currently showing a net profit in excess of  £ 150 K.

Whilst I can do the necessary calculations etc. a couple of matters have come to light which I really ought to sort before I go further :-

The client is adamant ( no paperwork forthcoming ! ) that the Contractor pays his Nat Ins !

The P/L A/c for the Sole Trade splits the turnover between the UK Sector & Non-Uk !

Have no experience whatsoever ( therein probably lies the answer ! ) of this Industry sector - can anyone point me in the right direction as HMRC's Web-Site is like sifting through treacle on these points.

Thanks