I think it all depends on where and what you are towing. I for one personally will not tow on the motorway if very windy as I think the cross winds are too dangerous. Whereas I have towed when windy but along your normal A type roads or roads a little more sheltered. Not sure if there any specific guidelines but would only tow in galeforce if emergency and needed to get to vets etc especially with lighter cargo on board.
I'm not sure in mph, but my yard is on the doorstep of a big road bridge and if it's closed to high sided vehicles, that's my cue not to take the trailer out! If it's restricted speed limit due to high winds/gusts, I'll consider whether my outing is really necessary or not.
I'm sure that's not very helpful to you though- sorry! There must be something somewhere though.