Thanks for advice everyone, ended up taking it to a recommended mechanic who said head didnt always need skimming, depended on any warping due to head cooling at different temps. Anyway, it needed a skim (4 thou") but the engineering firm that does all his work (the blokes an ex main agent mech. who now works from home) put it on a test bed, checked it, skimmed it and rechecked it then calculated what thickness head gasket it would need to keep the compression ratio the same and supplied one (they come in various guages apparently).
Afraid it sounds like it but the skimming of the head i`m not 100% with because the torquing of the bolts pulls the head flat again anyway! In fact i'd be asking how the garage can say it's warped before they remove it to see and i'd also be asking how they'll check it to find out........they should be using a surface table and dial test indicator/stand )I would have thought the reason for skimming the head would be more to do with removing residue from the old gasket so the heads nice and clean to take the new gasket. I once skimmed a mates cavalier head and his car didn't run the same afterwards and that was only removing .008 thou. ( remove any material from a cylinder head and you effect the compression )
It runs like a dream.