That already exists, in a roundabout sort of way. If necessary, something will be pinched to assist a failure clear of the running line - I understand that the ability for NR Control to request this and the means of compensating the operator involved is all part of the track access agreement. Perhaps someone else can add the details though (or tell me I'm wrong) - it's not something that I know a huge amount about.
I've been involved in two failed trains over the last few months, and in both cases assistance was rendered relatively quickly. One was a totally expired light engine being assisted in the rear by the following freight (just over ten miles at 10mph - so it still caused quite a delay), and the other was a DMU being assisted in the rear by a different TOC's DMU (with only about 25' delay to the failed train and minimal delay to the assisting train, despite the faff with assistance protection). It's not all bad!
I've been involved in two failed trains over the last few months, and in both cases assistance was rendered relatively quickly. One was a totally expired light engine being assisted in the rear by the following freight (just over ten miles at 10mph - so it still caused quite a delay), and the other was a DMU being assisted in the rear by a different TOC's DMU (with only about 25' delay to the failed train and minimal delay to the assisting train, despite the faff with assistance protection). It's not all bad!