Not an awful lot out there (using autotrader search) with a high seating position and >75g/km.

As well as your Mitsubishi there is the Kia nero. But if you want to throw in an MPV, the BMW 2 series active tourer is an option as is it's kissing cousin, the mini countryman phev. If you are in a position to go full electric, the renault zoe has a high seating position.

No idea about monthly lease rates though.

So close to being able to afford the XC60 or the XC90 both of which are great cars but then I think £800 a month is an insane amount of money to spend leasing a car. Our Honda CRV 1.6 DTEC SE-T costs me £259 a month on a four year lease with 10k p/a mileage allowance. It'll exceed 60mpg on a distance run, averages 56mpg day to day, costs £20 a year to tax and has all the room anyone could ever need. I can't see how a firm justifies spending so much. Nice if someone else is paying however. Out of curiosity, what fuel economy are you averaging on the Mitsubishi? We looked at them when we took the CRV but all the reports were showing real world economy was only a fraction of the official figure. These hybrids rarely stack up in reality.

Sounds like to me that the OP is getting a 'green status car', as I was under the impression that the 'under 75g/km' rule for CO2 has been scrapped for the zero rated VED band - its only actual electric-only (actual zero CO2 emissions at tailpipe) that now (for new ones at least) qualify, and besides, the next level up (for cars with a list price [including optional extras] of under £40k) is only £140 VED PER YEAR, hardly a big dent in the wallet of a firm, especially when they could lease a much better car of the same size for a significantly less amount (at least half that) and pay less in total when fuel, servicing and BIK taxes are added up.

It should also be noted that going for an expensive car, 'green' (not really [the PHEV's real mpg is an ave of 58 and ranges from 45 - 67mpg, plus where and how the electricity is mainly produced in the UK) which costs over £40k when new will attract a big penalty in VED. I agree with others saying they should just go for an 'ordinary' car suitable for the mileage/driving the OP actually does (not just to tick a box for so-called environmental reasons) that they find comfortable etc.

Not having a go at the OP specifically, but I've increasingly noticed that many company car owners, particularly upper middle and higher up managers are now spending HUGE sums on these vehicles (even under lease), which often takes significant sums away from the rest of the firm that could be better spent on productivity items for staff, and goes some way to stem the annoyance of lower ranked staff who see the same managers get more and better perks (most of which they don't need) as well as at least maintaining pay or getting decent rises, whilst they get nowt and struggle with 5yo deficient PCs and dodgy office chairs. I used to work for a small firm (it didn't earn a fortune) when the bosses, during the recession, bumped up their cars from mid premium saloons to top-of-the-range ones and 4x4s whilst asking us for pay cuts in 'hard times'. Needless to say this didn't go down well and was remembered.