Hampshires trucks can easily top 70+ on the motorways, unless they’re the bigger heavier ones. It’s fine to overtake if you can do so safely, however driving up our arse as it’s a short cut through the traffic is a route to disaster!
Appliance drivers have done an intensive advanced driving course that teaches us vehicle positioning and reaction skills, a slightly diluted version of the police’s, we drive anticipating everyone in front to do something stupid and they frequently do, but if there’s something behind us they may not be anticipating the same reactions and as you can imagine a fire engine is a pretty rubbish window.
I know hampshire has had several pumps in the workshop straightening the rear ends out as someone has fancied a short cut.
So in summing up, is overtaking a pump on blues on the motorway illegal? Not to my knowledge. Is it neccersary, only you can make that decision.