[Scuderia_Turini]

Hello Barrie,
If you are starting fom scratch and wanting magnetic rails you should consider Policar track instead of Scalextric.  Policar is slightly wider and has a deeper slot than Scalextric Sport. 
I am in the process of replacing my Ninco track with Policar and about 30% done. Policar is a rigid plastic construction so will not warp.  People have issues with the patterned finish of the Policar track surface and that the section joins are noticeable but the reality is that in use the look is soon forgotten whilst it provides decent grip and has great connectivity. The controllers and powerbase are fairly basic but you would want to upgrade those in any standard set system.  Track is available in the UK from Pendle Slot Racing and Jadlam.
Policar track has been designed and produced by the Slot-t team, info can be found here - Linky

Leo