Can't really
help here other than get the tyres you want fitted and not just a substitute because of some lame excuse. You want 452's, then get them ordered and fit them independently. You will find somewhere that'll do them but it will almost certainly be an independent.
I have an excellent relationship with my local independent who usually charge a bit less than Blackcircles do delivered as a fitted price. There are no monkey's there and have never had a damaged alloy. I've been going there for a good 15 years now.
They are based in Huntingdon which is now a 35-40 minute drive from MK with the Bedford bypass in, so just over a gallon of diesel and a bit of time.
Although I trust them with the prices, I always double check with Blackcircles just to be sure. The last two sets of tyres (B/Stone Sport Contact 2 - Seat - were about £9 per tyre fitted cheaper than BlackCircles could manage delivered, and the F1's for the Honda were about £3 per tyre cheaper fitted).
As they say with investments, past performance is no
guide to future results, but they may be worth a call and a trip.
If you want their number them PM me.