Stewart, I cannot recommend a repairer in the north, but this may be a job you can do yourself.
Turn the boat upside down at a height you can get yourself into the cockpit to see the deck around the mastgate. Clean the area up with acetone and put some glassfiber mat over the area, ensuring it overlaps enough to provide strength to the cracked area. Once it has hardened, turn the boat back and give it a polish. The cracks will not be a problem as the mat underneath will compensate. If you need to fill the cracks use a clear gelcoat having opened the crack up very slightly into a shallow V. This is especially difficult to do so is really a last resort. Before you apply and resins/gel always wash the area with acetone.
Good luck
Martin
