1. price - it's a hugely expensive vehicle
I think the whole EV price thing is an early-adopter issue. Need more economies of scale, and some scientific breakthrough / bring-to-market to both increase energy density, and thereby lower weight or increase range, and reduce price.
Sorry : stating the obvious.
he sees a £90-100 lower running cost due to the electric drive
A month? My back-of-envelope is that BEV compared to ICE saves £100 a month (on fuel) per 10,000 miles driven per annum. Depends on MPG comparison of course.
(Rough calculations: BEV does 3 miles per kWh, E7 around £0.08p per kWh [Tide is 6p I think?]. NextGen EV likely to get to around 4 miles per kWh - this is motorway speeds, not granny-driving

)
Fuel cost saving may not pay for extra initial capital cost, but higher mileage drivers have more gain. Someone driving 30,000 miles p.a. has £300 more per month to add to finance package. No idea what mileage a London Cabbie drives.
In terms of pollution etc. the choice will be to pay more for an EV or to pay a penalty e.g. Carbon Tax - for an ICE.
2. battery range. He was infuriated by the battery range - he said he's lucky to get 50 miles on full EV mode
I think PHEV may be the way to go for the next decade.
My EV does 220 real word miles. Commute is 80 miles per day, and I drive more than 220 miles a couple of days a month. Personally I would buy 300+ miles of range when it becomes available (not that charging is a pain, with ICE I used to spend more than 8 hours a year on forecourts filling up ... but I'd like the ability to "just do that unexpected journey")
But I think my requirement is selfish. I'm using less than 40% on my battery daily, and if instead 3 PHEV cars had a 1/3rd size of my battery they would be fully used on close to 100% of drive-days, and that would accelerate pollution-reduction and switch to Electricity.
A PHEV also takes away any range anxiety, and I think would ease the transition for Mr and Mrs Average Consumer. Also for car dealerships / maintenance.