They were also 2.9m wide (9cm wider than a Class 165) which could have caused a few clearance issues. In fact I'm sure I read somewhere that they were the widest carriages operating in GB.
I seem to recall that the loading gauge on the Tunnel and HS1 are nice and wide. Perhaps the answer is to install third rail DC electrification between St Pancras and Paris to give the old sets something to do
Ok, if loading gauge is out for the national network then that is a definitive dealbreaker.
I am less persuaded by the assumption that their state of repair is unacceptable in terms of reliability, though I do not mean to question the experience of anyone involved in operating them who may have posted above. Has the Metropolitan line been plagued by train failures in recent years? My assumption is that the LU fitters deserve more credit than that.
It is conceivable that reliable stock would be scrapped if running costs (routine maintenance, electricity etc) were too high in view of technological advances and the high daily mileage and hard duty that LU stock has to perform. By contrast, for an EMU on a branch line running peak relief services, the fixed leasing costs would logically account for a much greater proportion of per mile costs relative to the variable operating costs.
So a vehicle that you can buy for scrap value at the expense of relatively high operating costs could be very attractive in this situation, provided it doesn't actually fail all the time.
FWIW, the set used on the fairwell tour was clocked at 74 MPH, according to the correspondent from RAIL, but they are usually limited to 50. I wouldn't be suprised if this was down to crashworthiness. (LU may have judged that a trainload of enthusiasts and rail journalists were up for the chance to die happy)
... Anyway, gauging problems seem to be the killer. Oh well
I presume the bodies of the new units are built to the non-standard loading gauge? Or do they just have protruding doorsteps to reach the platforms?