Average home electricity prices are 0.29/kwh in London. The street lamp charging costs 0.24/kwh, so actually slightly cheaper for most people than charging at home.

By comparison, a Telsa Supercharger will run about 0.65/kwh here (but is obviously faster) and other brands I've seen as high as 0.85/kwh for rapid charging.

However if you agreed to an electricity plan where you pay floating hourly rates and you can charge at home with the right equipment, you could in theory pay less by only charging at low rate times overnight.

But given the the limited amount of driving I do (basically just weekend trips), the street charging costs are usually so low as to be a rounding error so it is not a big deal either way.