I've just renewed mine (2.5 Auto). The ones I took out were NLP100290. I got a set from Howards Garages for £23.98. Guess what? Same plugs, NLP100290. Someone had said they were cheapies, non-adjustable, non-Rover. They are adjustable and Howards guarantee them as Rover recommended. So I guess they must do the 1.8 version.
www.howardsgroup.co.uk