I thought I could shed a little light on this matter concerning BL policies and practices of the time, as I was a development fitter for the Rover group between the years of 1979-1990. To cut a long story short at the age of 16 I started my apprenticeship with BL as a development technician. Our on-the-job training involved moving around the various plants and satellite plants learning aspects of R & D engineering. The end product was to find a development department you would like to work in, for when you came out of your apprenticeship. I have some great TR7/8 stories I could tell you but I will save them for later.
The easiest way for me to explain the evolution of an experimental car and the reasons why they are destroyed, would be for me to start at the beginning. Taking a new car like the TR7
as an example:
1. Mock-ups After the initial drawing/approval/clay models. The first handful of bodies will be hand built, every panel will be made by the 'tin shops'. Press steel Fisher/Longbridge body division. These cars are a jumble of misfit bits, some components from other vehicles, some components made of wood like the engine, etc. Some part no. experimental no. exp chassis no. identified by project no. eg. 'bullet' these will be scrapped for prototypes.
2. Prototypes Cars not much better than above. Fitted with suppliers experimental parts. The cars would be a possible runner but not complete, held together with pop rivets, tape, wire, etc. Definitely not roadworthy. Would have exp. part numbers all over the place and exp. chassis no, may have ran on test track, limited no. built. Would be scrapped.
3. FEP's (Further Engineered Prototypes) Most vehicles fall into this area. Sometimes known as DEV Vehicles - short for Development Vehicles, or DD's - short for Development Derivatives. Bodies are being pressed out. Again not complete, but getting there. Still held together with tape, etc. Would be lent out to suppliers for fitting an exp. part. Some are roadworthy. Would run around on trade plates with camouflage. Every department would have 2 or 3 each. Would have exp. chassis no. but would be identified by the FEP no. in the windowscreen at the top and not necessarily the chassis no. Would be scrapped.