Get legal advice.
Assuming this is an ast (I do not know about anything else)
1) you can issue section 21 notice giving two months notice to quit. If the statuatory period has elapsed or will elapse by the time the notice comes due. IE if a 6 month ast you can issue before the end of month 4 so that it coincides with the end of month 6. It is only valid if issued on or before the rent day. So if the contract runs 11th of the month (assuming this flared up yesterday) then you can issue s21 now, and it will be two months from the next rent day 11th march – so out by 11th may.
2) Or you can issue section 8 notice using ground 8.
Used when the rent is still in arrears on the date that the Section 8 notice is served and on the date of the hearing. Where rent is due weekly or fortnightly, at least 8 weeks’ rent must be in arrears. Where rent is due monthly, at least two months’ rent must be in arrears. Where rent is due quarterly, at least a quarter’s rent must be in arrears by more than three months. Where rent is due yearly, at least three months’ rent must be in arrears by more than three months.
But section 8 it is not mandatory so you will have to go to court, this may be quick under accelerated possesion.
In the event the s21 notice is valid and elapses, the tenant may decide to stay, then you need to go to court to get an eviction order.
Learn the rules, get your ducks in a row, suck up the pain, move on.