The issue I found when deciding between new and nearly new is that you could actually pick up a brand new car for cheaper as it'll include the £1500 deposit contribution and further discounts through sites like Carwow and DTD. Depends if you want to wait 4-6 months or not. Also if you're going down the PCP route then APR is usually better on a new compared to used.
This is exactly what I have found. I got quotes through carwow and a brand new car with all the options I want is actually cheaper than an 18 plate low mileage used car without the options!
Given the residuals, I've found that cars have to be about 2 years old before sufficient depreciation kicks in to make them the better option cost wise. If I buy used middle of next year instead of waiting six months for delivery of a new car, I can get the facelift 7.5 for enough less money that it becomes attractive.
Buying very nearly new though seems to make no sense.