Rob the only acceptable repair IF its in the tread area is a Combi plug, sometimes called a Donkey Dick. Its the only method that tyre manufactures recommend and they're safe!
Some dealers will put a patch on the inside and then put a tube in the carcass and tell you its fine-' we do it all the time' what they won't say is that it reduces the tyre life and allows water to get into the carcass and it will then rust the steel in the tread belts-and they get to sell you a tube which in 99% of the time you don't need.
If its in the sidewall they are not legally repairable and any reputable tyre dealer should tell you that. Mind you some will take your money and not say a word.
Hope it helps
Rog