Britrail Pass Discount for Eurail Pass Holders

I have noticed that a discount is given on Britrail passes for 'current' Eurail Pass holders. My interpretation is that the Eurail pass must be validated in order for it to be 'current.' If I take advantage of the discount, but travel to Britain before I travel to the continent, is there a way to validate my eurail pass in Britain so that it is 'current'? Or will the Britrail officials not care if the Eurail pass has not been validated yet? Thanks!