How much notice do I need to give my landlord? (UK)

I know the law is due to change in May 2026, where it will be necessary to give 2 months notice.

I was originally on a 12 month contract but I asked to go to a rolling one this summer just gone (though they never actually gave me anything new to sign, I assumed it was not necessary). My original contract is 1 month’s notice.

My new tenancy agreement starts on March 1st 2026, and I currently pay rent here on the 1st of every month.

Is the end of January too late? He’s not been a very good landlord but I still feel weirdly guilty about not leaving them more than 30 days notice. I also don’t look forward to having people come view the flat while I’m still here, especially any longer than necessary. The flat came unfurnished and I begrudge him tricking anyone else into letting it by using my decor…

\*I write this while shivering in my poorly insulated, mice infested apartment (the building needs knocking down and burning) ((not my fault whatsoever, I’m *very* tidy - also who knew mice could get to the 1st floor?!))

Any advice appreciated. I know I probably need to not feel guilty. Thank you :)