I'd hazard a guess and presume they mean that should you be offered a position, you would be required to convert to a UK issued EASA licence if you don't have one already. While I don't want to get into why they ask this, I will say the majority of airlines ask the same, for example RYR ask for Irish, EJ/BA/VAA all ask for UK.....What I would say is, it'd be unreasonable with that in mind that people convert their licence from a non UK issued one just so they can tick that box when applying for VAA- and potentially jeopardise their position with their current airline, as well as spending time on money on a licence conversion they most likely won't need if unsuccessful with Virgin...