Intelligent Octopus is open for signups (I believe!) and offers 10p/kWh for some hours overnight and longer for the EV if you let them schedule the charge.

There's also Agile Octopus if you just want cheap off-rate. You might need to sign up to Agile then switch to Intelligent if you can't do Intelligent directly.

Both require a working smart meter.

You'll need to call Octopus in order to switch, their online signups have been suspended (like everyone else). My referral ID is fresh-cub-249 if they'll accept it over the phone, gets us both £50 credit.