Nope – being VAT registered means you only have to act as a tax collector on income from within the UK itself. You will probably find most of your affiliate income comes from offshore so I would suggest not registering unless you have to (Ie: go above the 50k threshold or whatever it is these days). The downside is that you can’t reclaim VAT on goods you buy in the UK and put through your company, but unless thats high value it’s still worth not being a government tax collector. Been there – and its a total pain in the arse.