File your crank profile.
Out of interest, do they fit on the other side? Oh, and TA are not exactly cheap.
Thanks, 'crank profile' was the phrase i was looking for. Not tried the other side as the chain line would be out, but I suppose if it fits there it might rule out the idea that the chainring is not round? yes, the TA was £40 but I got a discount at Condor, so not cheap.