GM Semi Synth.
£40.89 inc VAT from dealer if you have access to Trade Club
That is for 4 x 5l cans 
Why Semi and not fully, out of interest?
Not asking to be an argumentative SOB, honest
it's just that I always twitch when I hear 'semi synth' and I wonder why not spend a little extra for fully synth..
You should enjoy reading this:
http://www.omegaowners.com/forum/YaBB.pl?num=1200997700
I had a feeling that would be a link to one of Guy/Simon/Tim(I think?)'s posts

(Incidentally that's where all my oil comes from

)
I suppose I can see that on a non-turbo road car, fair point 
Depending on the turbo, still valid. For a diesel, definately. For a high performance petrol turbo, I'd probably change the priorities on life/performance/properties.
Indeed - the MR2 gets fully synth from Opie, changed every 6k and/or after an extended session on track .. but it sees a hard life given it's putting out anywhere between 50 and 100% more power than standard (depending on how far the
red mist descendswick gets turned up) with an oil-cooled plain bearing turbo

Anyway, I digress - can't argue with the price of the GM oil on the trade club, for sure.