Just had a play with the My2050 simulator... my first attempt got CO2 really low ... then I realised I had no balance between supply and demand so I played around again. This is where I got to. What would you do differently?
I also just made an attempt, and first I got to the same point as you, Jo: I didn't meet the energy demand. With the adjustments I made, I reached the target and energy supply exceeded demand.
There are a few things that might be a long shot, other are not necessarily.
In my simulation I am expecting that 3 out of 5 cars are powered by electricity, which sounds crazy right now and might be a little to ambitious. But then again, 2050 is a long time from now, so once the e-car industry picks up pace I can imagine such a development.
I set that 3 of 4 houses have additional insulation, which might out of reach, too. But I do not know any current numbers on how many there are right now. Does anyone know if the British state subsidises energy-related renovation in homes?