Thanks all, doe anyone have the phone number for the helpline several have mentioned? Will give them a call on Monday.
My gut thought now is that it's a great way to save for normal purchases. But for anyone doing a new build and looking to reclaim VAT, it's probably a risk not worth taking. I'll report back next week once I've spoken to HMRC.
Thanks all all for your help and concern, happy to be a guinea pig, worst case scenario is I've lost £190, quite a pain but I won't let it consume me if it is to be the case. I'll make that back Savings on other things in my day to day life now I've realised how many different gift cards I can buy through my employer.