Everyone's noticed that they aren't exactly holding their value as planned But what will they sell for in 5 years say? Well, take a look at 2nd hand prices right now for other high quality limited edition drivers' cars:

BMW e30 M3 evo, 10-13 years old: £7-10k
Audi Quattro 20v, 10-12 years old: £9-11k
Porsche 968, 5-7 years old: £12-16k

I don't think the P1 will have much trouble retaining similar values in 5-10 years time, so you are looking at 5 year depreciation of about £15-7k, and 10 year depreciation of about £20k. As usual the big hit is in the first year or two, so if you like the car but don't want to blow 5-10k in the first year, just get one 2nd hand and you shouldn't be too badly off financially.