That is broadly where I got to years ago. about a 3 times uptick in electrical grid to replace all fossil fuels with leccy.
The calculation is very difficult to do reliably, because there is the matter of fossil conversion efficiency to 'desired outcome' versus electrical efficiency to do the same. i.e. you probably need half as much electricity in energy terms to move a vehicle, as diesel.
And when we are talking about energy input to such things as fertiliser manufacturing or smelting, all bets are off. I simply don't know.
(Yes, you probably could smelt iron with pure hydrogen for example)
I think it will happen slowly to as much of a degree as the technology permits.
Right now electric cars survive on subsidy, but electric trains are cheaper than diesel ones once the overhead wires are in place (or the third rail).
In between the lines of DECC's reports is the tacit assumption that we will be using a LOT of nuclear electricity in the future.
Electric cars are perfectly viable for inner city driverless taxis, operating out of a charger base, and or low mileage shopping and school run second cars in the 'burbs.
It wont happen overnight, but behind the scenes plans to beef up the grid and add nukes to it seem to be being made.
And the ruthless drive for energy efficiency goes on - we now have LED bulbs. The new processor on my PC is 5 times as fast as the old and uses half the power. House insulation is about maxed out on new builds.
I would say that fracking is not rendering massive deployment of electrical vehicles and electrical alternatives out, but merely buying us the time to do it in a measured and steady way.
Green crap is on the way out, renewable energy is too expensive and dysfunctional - TPTB don't want their London mansions to have power cuts, so that means more nukes, lots more nukes, in the next 30 years. And a much bigger grid.
Unless of course we get a massive population die back....
...I am dreaming of a fatal disease transmitted by tattoo parlours.