As others said if your doing long distance commutes diesel is sadly still king.
Even plug-in hybrids don't reat return good mpg when you have to rely on the ICE engine. The Audi A3 e-tron has a claimed 140mpg, but when you deplet the battery (30 miles EV range), and use the ICE, the mpg falls as low as 34!!
http://m.caranddriver.com/audi/a3-e-tron
The BMW i3 range extender is similar, claimed 120 mpg, but if you deplete the 80 mile EV charge and need to use the ICE, real life mpg is no more than 40 :(
http://www.autoexpress.co.uk/bmw/i3
In my expericene of owing an all electric Leaf, a IS300h, and having recently spent 18 months commuting in 100 miles a day in a Civic diesel. If I was still doing 100 miles a day commuting I would be ordering a Tesla S.
The new 'basic' model has a list price of £55k, which is a lot, but list price for our Premiere Spec IS300H with the Lexus safety kit was around £41k. Given the Tesla has 100bhp more the premium over the IS300H is not horrendous. Tesla are making decent sales in the UK, I've seen two driving around where I live, so in 24 months time I expect used one to appear at a decent discount over new price.
So if you hold off buying now, I think your desire to own a hybrid/EV car that will offer you better mpg than a diesel on long M ways commute may be meet.....However if your commute is only 80 miles, a range extenderi3 may get you by on EV power alone, with the added safety of an ICE back up, i3 residuals are predicted to be 30% at 3 years, so worth having a look at a used one :)
Here's a 2 year old one, range extender, less than 10k on the clock, cheaper than a new IS300H....Don't you just love depreciation!!
http://www.pistonheads.com/classifieds/used-cars/bmw/i3/i3-hatchback-range-extender-5dr-auto/3925288