So far I've ignored the HMRC (not that they have tried to contact me) .. They either need to set out the law in pain English, or win a case against a spread bettor before i start paying tax. At the moment, my understanding is that its still very debatable, so i'm on the fence for now.
Any gains from spreadbetting are tax free because you are officially "gambling". Plus, you are actually effectively paying tax by using a spreadbetting company (who pay tax on your behalf) because they charge you thru wider spreads, etc. So you're paying it one way or the other. If you use a spreadbetter, you're paying tax indirectly.
A good friend of mine has a letter from HMRC saying he has zero tax to pay from his "gambling" (he has made a 7 figure number for about the past 8 years "gambling"). He made them write it so he could never experience a 'clawback'.