I've seen a few videos on you tube showing some Duro tyre's that are not round, as these are about the only road legal tyres in the size I want that are available in the UK should I be worried about buying them ?

It's always a throw of the dice on tires, no matter which brand you buy.
My buddy has a set of duros on his Yamaha ATV. When following him you can see that one of the back ones is just a bit out of round but he says it has no noticeable vibration.

Duro tires are one of the few brands that have a deserved reputation, and I don't mean in a good way. Some brands are cheap, but still a worthwhile tire. They may be few and far between, but they are out there. Duro are cheap, but not a quality brand. Since you specified road legal, I can't even offer a recommendation, but for offroad only, I will recommend a Wanda P350 (Bighorn knockoff) as we have some guys who are running those tires and they do a very nice job in the dirt and mud.

Thanks guys, I had been looking at Wanda tyres

This is a reply I received from a local Duro supplier-

We always advise inflating these to 30psi and leaving them for 24 – 48 hours in a warm room then adjust to desired pressure – they are always 'flat packed' for transport over here and need some time to get into shape – if used straight away they can give you problems like you have described.