I have had an SE for 2 months now, in the USA. You don't need to bend over and squeal like a piggy here to pay for electricity. Mine is about 9c/kWh!
My car showed up months before I was told to expect it, so I hadn't got the wall charger done. First I was charging at 110V, 1.4kW. Forget about trying to use this for daily use. If I was at home, I was charging. A full charge from flat is around 31h in summer. It may be worse in winter
Next I had a 230v 20A outlet in my car port. 3.6kW. That was bearable. 9 1/2 hours for a full charge. Finally, I got my wall charger in. 7.2kW, which is the max that Minis will charge at with single phase. US models only have a single phase charger. Now, I plug it in every two commutes and set it to charge to around 85-90% with a time slot on the EVSE. 1% charge every 2.7 minutes.
1 commute is 36miles, around 30% battery. Using the middle part of the battery will maximise life.
Charging immediately before departure also warms the battery, that will help range in winter. I'm noticing a difference in morning commute % even now, depending on whether the car charged before I left.
I also have a Tesla UMC2 as my mobile charger. The USA has a zillion different outlets and the Tesla chargers have 8 different adaptors. I made a 9th for charging at work... For US cars, the car end plug needed changing euro Tesla's now use Mennekes, so you guys are good to go. Max is 32A, perfect! Mine is actually an EU spec, which was almost free on US ebay...
Wall charger is openEVSE. This is an open source charger, so if you can code, it can be hacked to do things it doesn't currently do. It also means other people are going to add features down the line. Out of the box, I can charge in a time slot, charge a certain kWh. I believe it can also interface with other devices on the network that tell it when and how fast to charge. It can also negotiate with other openEVSE units if you have more than one, so they can run from the same supply and cable. I went for the 48A version so I would have plenty of power if I get a 2nd EV.
I would absolutely recommend having a smart wall charger, especially with the cost disparity of peak and off peak electricity in the UK. It makes charging a breeze, instead of a juggling act. A UK granny charger is what, around 20hours for a full charge?
At 7.2kW, charging efficiency from wall to battery is 90%. With 1.4kW granny charging, I was getting 65%. Charging appears to have a parasitic load of hundreds of watts that kills efficiency at low charge rates.