http://www.theguardian.com/money/2012/sep/10/do-you-pay-tax-...
HM Revenue & Customs doesn't regard lottery winnings as income, so all prizes are tax-free – hurray! However, there could be tax implications once you've banked your winnings.
I'm struggling to find other answers, the Daily Mail's 'This is Money' website says the opposite is true and that it's counted as freelancer income.http://www.thisismoney.co.uk/money/experts/article-2551709/I...
HMRC has produced guidance in the context of freelancers who win prizes and the short version is that they view most prizes as taxable income of the freelancer.
Grey area? An interesting area.