Has anyone go a good discount off the retail in the UK?
In addition to the referral code the quote you have probably includes the £5,000 government grant - but if not its a useful saving. Likely to be phased out soon-ish though.
Other than that Man Maths might help (same on the X as the S) :
With Economy-7 charging overnight and some supercharger recharging I reckon the saving is about £100 / month / 10,000 miles p.a. driven compared to Petrol / Diesel - if you drive, say, 25,000 miles a year that's £250 a month you can stick on the finance, if you can charge-at-work the figures are better still, particularly if your round-trip daily commute is less than the battery range
If its a (UK) company car you have 100% first year right-off on electric vehicle (not sure for how much longer) and (I think) about 50% of the benefit-in-kind tax of an ICE car - that's tapering off too, so best option, right now, is probably company-purchase and sell back to yourself in a couple of years time - with the company taking the main depreciation hit.
Might get some UK-specific advice int he UK forum:
The UK and Ireland