There were speed limiters fitted to all of them eventually. The fastest I saw one go was only 127mph (they hit full speed between Swindon and Didcot, as the line is very straight).
FWIW, it was believed in railway circles for 150 years that you couldn't safely propel a train at high speed from the rear. Push/pull steam units, with a driving cab in an autocoach, were common but were very sedate. Eventually, testing (by BR, for the Class 91/IC225, I think) showed this was all bollocks. At model train scale, pushing lighter carriages does indeed lead to more derailments but, at full size and weight, it doesn't. An IC225 is being pushed half the time, and driven from the DVT (driving van trailer, not deep vein thrombosis).
The unluckiest Class 91 has just been scrapped; it was involved in both the Hatfield and Great Heck disasters. Neither were due to any fault with the locomotive.