The trick to getting wheels cheap, is to find out who the UK importer is. The importer is who all the other dealers get their supplies from. Unless, of course if the wheels are made in the UK, then approach the manufacturer directly.
I got my wheels direct from the importer, and saved £200 against the next nearest quote. Basically this was the margin the dealer was making. You might need to do some haggling, to get discount.
But try charm

caws that works too.
You must also make payment as easy for them as possible. After all, they are doing you the favour of charging less. And this could end up being the reason you get the discount. So either offer a bankers draft or cheque. Cash or Credit card usually causes them hassle, and in the case of Credit cards costs them money.
To really make the savings, arrange collection yourself. Unless this is more difficult for the seller to do.
Of course, some wheel manufacturers sell direct to more than one importer, or cut him out, and sell direct to the dealer. In these cases it's harder to get the discount.
So that's a Group Buy on wheels anyone.!!

Only joking