Thanks all for your help and input and also to NMA Tools Technical help line.
To complete the story the blade was 0.4mm of alignment with the mitre slots. It is adjusted as per the suggestion above, from underneath the saw. It can be done without turning the saw over.
Remove one of the bottom sections of the side cover by removing the four screws. The blade mechanism is held to the underside of the cast iron table by four 13mm hex head bolts. It is also held by two mild steel plates, front and rear, of the mech. with one 13mm bolt each. Loosen all 6 slightly so there is still some ‘drag’ on them. Work out which way the blade needs to move to correct it. Tap the mechanism at the relevant fixing point with a light hammer. Until it the blade is aligned. You will need to keep coming out from under the saw and check the alignment. Once happy gently tighten all 6 bolts. They were not particularly tight when I removed them so went with a gentle nip up with a ratchet.
The side cover can be replaced with the help of a magnet or suction pad to help hold it in place while the screws are done up.
Took about 20minutes and that was the first time. You can also hoover all the sawdust from the inside that the crappy dust collection leaves in the cabinet.
For reference NMA Tools reckoned 0.2mm difference across the blade was ok but 0.4mm probably too much.
Thanks again and hope this helps someone out in the future.
