Well in the end it turned out that the head on the car was indeed very well ported already! The cams were BD14s. Got the whole head rebuilt anyway with double valve springs.

The reason why the car wasn't producing the power was that the timing was out on the inlet cam. So much so that it was only the pockets machined into the pistons that saved impact. I took this matter up with the firm that did the work on my car and then mapped it and they basically told me that they never check cam timing and fully washed their hands of any responsibility. They were happy to take my money but not happy to accept that such a basic issue should have been checked.

I am unable to mention names in this forum but if anybody wants to know who (to avoid!) then PM me and I will let you know.

When it was rebuilt (by a chap called Piero Dicapite in Essex who I highly recommend) I took the car to Engine Advantages in Essex who after sorting out a couple of minor misfires, discovering that the pectel board that I had supplied the previous mappers was not there!, mapped the car succesfully to 485 bhp. I would recommend Engine Advantages too, they were superb and Piero even popped down to make sure everything went ok!

No quite the 500 but it feels pretty good anyway.