British professional gamblers should pay income tax.
I agree in principal but the enforcement and paperwork associated with this would be a nightmare and would probably cost way more than it generates. Kind of like how the state pension/free TV license isn't means tested so just given to everyone even if they are multi-millionaires.
Also the amount of professional gamblers is actually quite small, how many in total in the UK? A few thousand? The govt still rakes 50% of income in live casinos don't they, and 15% of online profits? Most pro gamblers will have paid more in tax than the avg person via this route, plus the makeup demographics of them will mean that they don't use as many public services as the avg person too (male, between 20 and 40 and without kids).
The average pro gambler def lives in a bubble and they should donate to charity or volunteer tho as its a very selfish industry and perspective is required.