The cost of tax in the UK currently ranges up to 40% (50% from April 2010) and can take a significant chunk of trading profit from you over time. So there being no tax or CGT on spread bets is one of the biggest advantages of financial spread betting over normal equity or CFD trading. The profits you make are completely free from UK capital gains and income tax as they are treated as gambling, and therefore fall outside the scope of taxation. (Tax Laws are subject to change).