I am planning to get a set of 14" BBS's off joshimitsu in the near future.

Considering my car has alloys as standard, in what way will this affect insurance?

My dad organised my insurance when it first began, but he chose Tesco, probably as he works there (even though his BMW is on some kind of classic car insurance and my brother's polo is on adrian flux), although I am a named driver and he is the main policy holder, which comes to about 800 a year.

What are the odds, first off, that tesco will chew me up and promptly discard me for this particular modification? And secondly, am I certain to get a cheaper quote elsewhere with one of the discounted organisations, wheels or not

As they're non-standard they'll most likely shew you up and spit you out...