Further to my post of 18 April, I have investigated further the cost of future services for my Lexus IS 300H.
A four year service (interim) would cost £175 at one Lexus dealership, yet cost £275 at another Lexus dealership only 40 miles away from each other.
A five year service (full) at the same dealerships would be £355 at one, and £485 at the other.
Interestingly, a two year extended warranty would cost the same at both dealerships, namely £795.
It rather looks like I will be changing my dealership!