Thank you Matt,
Further investigation from three local tyre dealers/fitters finds that in their records and back listings 215/45 are indeed the correct tyre. It seems the only reference to the 215/50 tyre is in the Toyota handbook. One tyre dealer actually said the the problem with handbooks is that they are generic. One would have thought the manufacturer would know what tyres they specified. My nearest Toyota main dealer is surprisingly vague on the subject.
The same car (different model) is available with a 16inch wheel. Although I haven't looked into it at all, I wonder if this is where the confusion might lie.
In any event, I have ordered 4 new 215/45 Goodyear Eagles (for the lowest noise rating) they are to be fitted tomorrow (04/12)
As far as the 3.3% speedo error is concerned, would that be faster road-speed or slower than that indicated? just curious as in practice I wouldn't think in general use it would make much difference unless I was using the cruise control at the legal limit.