Also
@Phil752 do you mean Fast or Rapid? There's a big difference

For Fast charging at supermarkets, it's usually nothing. No charge, and if you have the time and it's convenient, that's obviously the way to go.
For Rapid charging, expect 30-35p / kwh as being the usual, PAYG standard (which I consider expensive), or maybe Polar at half that plus a monthly subscription. I don't know about any other networks.
Let's do some calculations based on 30p/kwh assuming there is no additional (connection) charge which some networks might add.
Every 10% you charge it up, it's going to cost (44.5 kwh total capacity * .30p cost per kwh) * .1 (ten percent) = £1.30.
If you arrive with 20% charge and take your car up to 80%, that's 6 * £1.30 = £7.80
Or 20% to 90% will be 7 * £1.30 = £9.10
Approximately.
I used to use a Polar card which is £7.50 a month and then 15p/kwh at 50kw rapid chargers. Obviously you have to do some maths to figure out whether or not it's worth paying this or just PAYG (I cancelled mine because I haven't gone anywhere during lockdown).