Just look what plant they are using for the replacement job then? no very large road mounted cranes to be seen. Its just the good old breakdown cranes from the nearest loco depot,s one most probably been Doncaster Carr Loco,s crane and the rest of the breakdown train just in case it had to go to a derailment.
In them days all the cost was kept in house in this case instead of hiring in large road cranes needing bases constructing beforehand.
Actually the bulk of the work done with the heavy breakdown cranes was always jobs for the engineers; derailments needing the "big hook" were actually few and far between, most just needed the tool vans which contained jacks and ramps etc. Sure, they were always kept on the front road of their loco depot, mainly for ready availability of a loco to go anywhere, but most of their work was planned in advance. There were various procedures if there was an incident while they were in use, just like there were if you were unlucky enough to get two incidents together, or one which needed two cranes (as big civils jobs often did).
I've forgotten where the big hook came from for Taunton jobs, something tells me it was Swindon. A photo I recall of the crane once overturned in Swindon scrap yard attempting to pick up a boiler from a scrap loco shows there were all sorts of things to use them for (presumably the Old Oak Common one had to come and pick up it's sibling).