Thanks guys - I guess Sh1t happens (trying to be philosophical about this - but it's hard)
I've checked the tyre and the damage looks superficial (just a tiny tear in the outside rubber but it's only a mm or so deep (so no chunk missing or flap of rubber), but I'll get it checked out anyway.
My plans are (I think) a) to buy a replacement Brescia alloy (I've seen a brand new one on the bay from a VW dealer for around £350), get a new tyre on it, then use the existing one as a "spare" (might get it refurbished - might not - as it's bound to happen again !
Or - get the alloy refurbished by Lepson's at a cost of £128.40 (inc VAT) plus maybe add a new tyre for safety (around another £150 ish) so £280 all in - bit of an expensive morning !
I know the Lepson's route is cheaper, but I'm thinking if this happens again, buying another wheel and having a spare (refurbished) might come in handy.