Thanks for your question - I am Sam and I am one of the UK tax experts here on Just Answer.
Whether this is full time or not, HMRC will only consider his a trade (and therefore liable to tax) if
1) You place bets for others using their money and earn from this
2) You are part of a syndicate
And that is the position is the terms of the contract and the economic substance of what is done, refers to
Other then that, in the main gambling (which this still falls within the cope of) is not liable to tax, and whilst profits (gains) are not liable to tax, losses cannot be then claimed either.
Let me know if I can assist further, but if you have all that you need, then it would be appreciated if you could rate me for the level of service I have supplied (or click accept)