Otter's Pocket,
Sorry I can't point you to where to find this info, but any accountant should be able to advise. You could try PM'ing Whirlygig 'cos she be a numbers wizzard
Above a certain threshold VAT registration becomes mandatory, but there is nothing to stop you registering voluntarily. This I know to be true as I'm VAT registered. Initially as an FI, more lately as an onshore corporate pilot