Insects seem to prefer some dogs to others ! My current two run free in the woods and fields and never have any bites (am also in UK). But in the past, some of the forefathers of this generation have suffered badly - which is why I carry Piriton with me. Half a tablet seems to calm the itching very quickly without any harm to the Basenji.
I used to go to shows with another breeder and one of her girls was fine until we crossed the border into Scotland - and then she broke out in lumps and bumps and often couldn't be shown. Never happened down South !!!
I did once try 'shirts' but on the boys they were a darned nuisance ! there was no gap so they could pee. I gave them up in short order and am glad these two oldies seems to be immune.
But try Piriton - only don't tell the pharmacist what you need it for. I once (in Boots the Chemist) made the mistake of saying I needed the antihistamin for the dogs. Whereupon the packet was hastily withdrawn and she refused to sell it to me. "Can't sell you veterinary preparations, this is NOT for animal use", was her excuse and no way would she sell me any. So I went next door to Proctors and didn't mention what I needed it for - no problems !