Correct me if im wrong ray, but holiday pay is a legal requirement for all employees, and full offshore rate would include salary portion too!
Consider yourself corrected.
From the Unite Union latest news update:-
"WTD HOLIDAY LEGAL CASE
The ongoing legal argument on holiday entitlement for drillers is now proceeding to the Court of Session in London.
The Unite legal team will present their appeal in writing on September 2011 and the case will be heard on the 26/27th October 2011 at the Court of Session. A result should be known five or six weeks later."
And
http://www.bbc.co.uk/news/10316549
And even if holiday pay is forthcoming, it is more likely to be you are entitled to your basic pay, not your basic pay plus offshore allowance.