Good look on your potential career choice! I don't know what experience you have playing poker, whether you are a seasoned amatuer or a complete beginner, so you may need that luck!
Also, you don't say whether you are a native of the United Kingdom of Great Britain and Northern Ireland, which is the name of the country, abbriviated to UK (England is just one nation within the country. There are two nations of the UK, a province and a principality. England, Scotland, Northern Ireland and Wales, respectively).
I say this, because the advice I can give you depends party on your status. You might be a professional poker player from the USA, relocating to England and seeking advice on how to pursue your career over here. Or, you're a young adult whose lived in England all their life and just recently reached legal age to gamble. You've been reading guides on how to be a professional gambler written by an American and confused by all the talk of registering your tax status! More information would be helpful, but I'll try to be neutral and give you an answer that's helpful in any case.
FYI the most important thing to note if you want to play poker in the UK is that, unlike the USA, your winnings are tax free.
All games of chance in the UK are not subject to taxation, meaning you'd not need to register with the taxman or worry about tax codes or anything like that. Whether it's the national lottery, gambling on the football pools or betting on the Grand National (or any other) horse race, any money you win is not subject to tax.
However, if you are lucky enough to have a significant bankroll sitting in a bank account earning interest, or in an ISA or invested as some other financial investment option, the income earned from interest IS subject to tax!
That's not going to matter if your bankroll is spread across online poker sites, or sitting under your mattress in piles of banknotes ready to take your local brick & mortar casino, none of these earn you interest.
Many poker players will have side activities related to the game, but off the table. Being a coach for other players cand charging a fee for the service. Maybe they manage a stable of professional poker players or run a website such as pokerstrategy.com selling advertising space on the site or offering deposit bonuses to players who register with partnered poker networks using a bonus code unique to them.
ALL of those side activities WILL be subject to tax, as they are all classed as income, as earnings related to business activities/employment.
Knowing the difference between income and winning will keep you on the right side of UK law and off the radar of His Majesties Revenue & Customs and the Department of Work and Pensions (DWP).
Mentioning the DWP, you might be interested to note how your poker activities might affect any unemployment benefit youmay or may not be entitled to. Since "poker player" is not a legitimate form of employment for the purpose of tax, the job centre is not going to take kindly to you declaring you've spent 60 hours për week for the last month playing online poker and zero hours looking for a real job!
You can and should claim Universal Credit if you are not working a real job. As well as £300 a month credited to your bank account, your rent and council tax will be paid for whilst you are not gainfully employed.
SUBJECT TO THE CONDITION: that you agree to participate in a certain number of hours a week looking for a real job. In practise, this means you will visit the job centre once a month with evidence that you have looked and applied for one or more position of employment. Your search history & application record from indeed.com often will suffice, and your visit is 5-10mins long. You might have spent only 1 hour all month doing this, they really don't have enough time to check in depth - just don't say you've not been looking because you're too busy playing poker.
SUBJECT TO SAVINGS: you are allowed £6,000 in savings (such as your poker bankroll) and your Universal Credit will not be affected! Once you go above £6,000 then your benefit entitlement will be adjusted on a sliding scale for each X amount over the £6k, for example you lose £1 of benefit off your monthly £300 for each extra £100 over the £6k - your rent and council tax will not be deducted unless and until your cash entitlement reduces to zero.
Can I legitimately declare myself as self employed so that I don't have to commit to avtively seeking a "real job"? YES!
What's more, you can STILL claim Universal Credit whilst doing so!! You will be allocated a small business advisor at the job centre, who will assist you in creatinga business plan.
You can claim Universal Credit unaffected for 12 months whilst preparing to start your business. You cannot just say "I'm going to be a professional poker player" - you will have to explore all the legitimate business options that relate to the game, as I mentioned above, like being a coach, running a poker youtube channel as a poker content creator.
Once your business is trading, you have to declare your income to the job centre on a monthly basis as a self employed individual (or director of a limited company) - for the month(s) that you earn below the living wage, you will recieve the same Universal Credit you would have gotten as an unemployed person. This reduces on a sliding scale similar to if you have savings in the bank, with your rent entitlent the last to be reduced.
Additionally, as a new business, you will get an additional payment, for the first six months after you start trading, paid as a grant applied on top of your Universal Credit that is NOT adjusted for earnings!
Since poker winnings aren't classed as income, but winnings, you cannot declare your poker playing revenue as business earnings for the purpose of declaring business income to the job centre. But all those other side activities will count, and be subject to tax at the usual rates.
You don't have to claim Universal Credit (or sick benefit if you have a legitimate physical or mental impairment that prevents you from being gainfully employed) but equally, you would be insane to turn down free assistance if you qualify for it!
If you earn enough from poker playing alone to cover your rent, council tax, utility bills (electric, gas, broadband) and other living expenses, then you are likely to have a bankroll big enough to disqualify you from claiming Universal Credit in any case!!! If you do, well done and good luck. Keep records in case the taxman wants to know where the money comes from. If you don't earn enough, then claim what you are entitled. Just DON'T lie! If you win an MTT for £150,000 (meaning you'll have above the allowed £6,000 savings) and fail to report the change in circumstance, the DWP and Local Council WILL pursue you to recover the over payment of rent, council tax, and take you to court where you may well recieve a custodial or other punitive community sentence.
Everyone else would be crazy to turn down the assistance.
Finally, I am not advocating using unemployment benefit to fund any gambling activity. Even more so if you have dependants (wife, children) who rely on that monthly payment with which to live.
You should never gamble with the housekeeping. Play with what you can afford, and only after your monthly expenses have been deducted from the monthly income(s).