My absolute all-time most bestest favourite comedian is Chris Morris (Brass Eye, Jam, Four Lions) - who is a genius whose work is still blisteringly modern today even though most of it was recorded 25 years ago now. The way he uses neologisms is pure trip-fuel too if you enjoy banned substances.
https://youtu.be/r3BO6GP9NMY, a little sample.
https://youtu.be/0lhJ3YJkfcg longer but more insane sample
He's not really a standup though. I think Norm was probably my favourite long-form standup all things considered, and it feels slightly weird comparing him to a British one because although he definitely reminded me of the subversiveness of comedy this side of the pond, he was still very much an American comic. Comedians over here are typically much more personal if they do "bits" (i.e. expertly performed but often true stories), or just pure one-liner merchants. Similarly, "improv" has always seemed very alien to me.
If I had to pick one pure standup it would have to be Frankie Boyle just by the volume of laughs I've got out of him.
If you want endless hours of fun British comedy (mostly improvised, I'm a hypocrite), listen to a little of the old Gervais, Pilkington, and Merchant radio shows from back in the day.
I get it.
Benny Hill: real
Doug Stanhope: fake