Cheers for this jack,
Long story behind this.
The alternator was mounted a couple of mm to the right so therefore the pulleys didn't line up. 300 miles later in pasing Carlisle and there was a clunk clunk ping thwack noise, left the belt on the M6 managed to get to glasgow and drive to halfords, me and my mate had a snoop behind the alternator to see if it could be moved any. I thought i needed a small block alti hence the request and i wasn't going to buy a recon unit from halfrauds! Then we noticed the tensioner had a silly spacer for some reason. promtly removed it and hey presto! when we tightened it up the alti moved the required 5 mm
Thanks for your help though jack

next time i see you!