I guess the UK policy may be different from the US one, but when I crashed my Giro I had to send in my crashed helmet, a copy of the receipt for said helmet (which, amazingly enough, I had squirreled away), a cheque for half the retail value of my helmet and a detailed account of how the crash occurred. Then they send back the same model of helmet or an equivalent if they no longer make that model.

I think they must have liked my story, eh - they never cashed my cheque.