I know this problem well from trying to get cover for a BC26. Many recovery services limit the length to 7m. A further problem is that even where length isn't limited, the maximum width may be set to the old legal maximum trailer width of 2.3m. The law changed some years ago - and with a 2.54m beam the BC26 makes the most of the new 2.55m limit - but many recovery companies/insurers, e.g. the AA, have not changed their terms and still specify a limit of 2.3m.
As an aside, I notice that a BC23's beam is just over 2.3m so this width issue theoretically applies to BC23s too although at 2.36m beam you'd have to have a very pedantic recovery driver (and armed with a good tape measure) to fall foul of that limit!
Two services we have found that accommodate the BC26 (unlimited length, up to 2.55m width and weight limit of 3.5T) are RAC Arrival and Green Flag Mayday. I would be interested if anyone else knows of services that cover a BC26 because our renewal is due this month...