Tesla make some of their DC chargers publicly available and the pricing is only expensive (at the right time of day)- you will need the Tesla app.
Otherwise as hc25036 posted, the Electroverse app is one of the more useful, it shows Lidl chargers, if you have the Lidl app for your shopping and pay using it they are 62p per kWh for DC rapid charging and 40p/kWh for the 7kW "fast" charging. (Still hugely more expensive than home charging, even at standard rate, horrendous if you are used to 7p/kWh!)
The Lidl needs to be open though and there will be a limit on your time in the carpark, but half an hour rapid charging will be fine.
Tbh, if you would have to pay 80 odd pence per kWh to rapid charge away from home you might as well just run on petrol for the same sort of cost per mile and not waste time charging. (Can you charge by regenerative braking when running on petrol?)
Most of the charger networks do a subscription service where you shell out every month and get a discount on their extortionate prices, but you need to be doing a lot of rapid charging to make it worthwhile.
EDIT: Whoops! I put Aldi by mistake, their chargers do show, but I don't know their prices, I tested that my car will DC charge with £3 worth of Lidl electricity, I won't be buying any more unless the choice is pay or walk home....
