i bought a set of 500 wheels and tyres so I could put winter tyres on the steel rims. The 500 set came with as new 175/65/14 Michelines. Can I sitck these on once the current summer tyres are done - it runs 185/65/14s usually, but not sure if the 175s are an "officially allowed" alternative.

I ran my 4x4 on 500 winters in that same size, you should let your insurance company know however.