We're confusing two issues here.
Their refusal to recover a trailer with an overall length over 7mtrs is not because the trailer isn't road legal.
My friend is an RAC recovery truck driver and they are not allowed to recover a trailer with an overall length over 7mrs. RAC rules....nothing to do with the law.
If it was a legal issue, Green Flag wouldn't be able to flout the law just because you are a member of the Caravan Club and gave them an extra wedge of cash.
This is where my fight with Green Flag started. When I signed up I ask what their trailer policy was. I was told "they would recover any trailer that I was lawfully towing" then I read the small print, phoned them.....their story had changed and I was refunded the balance of my subscription.