Never one to give up easily, I cut a tyre of one of the wheels this morning , and there was no band fitted. Bear in mind this is an original tyre and wheel, never been off for puncture repair. I took this rim back to the same national tyre company and asked if they would now fit 4 new tyres to the wheels if I took them off and brought them down. Astonishingly, they said that although that wheel didn't have a band, the other 3 might so they couldn't guarantee they be able to fit the tyres. Quite why a company would supply and fit bands to some but not all tyres on a trailer is anyone's guess, but at this point I decided that this company didn't actually want my money, so left.
Regardless of any perceived merit for the bands, the trailer has never had them from new. As its a double axle, I'm not going to have bands retro fitted, and have decided to go for 4 new complete tyres and wheels for marginally more than the 4 tyres would have cost.
What a foccin palava