Saying Bitcoins is vouchers is wrong in my eyes. Only discount vouchers that are sold are Vat-able, all other vouchers are VAT free according to HMRC. So if Bitcoins are vouchers they are not Vat-able. I do believe that they are not vouchers and HMRC regardless of what they have said in the past will not treat them as vouchers.
This is simply wrong. Bitcoins *are* a VATable commodity and HMRC *will* expect you to pay VAT if you meet the threshold. Wishing on rainbows and unicorns that you'll be a 'special case' is willful ignorance.
See:
https://localbitcoins.com/forums/#!/regional/uk#uk-sellersbuyers-beware
Remember; Ignorance is no excuse in the eyes of the law.