Best reason to leave the EU would be not using the Euro anymore, but Britain never gave up the pound in the first place, so that's not an issue. Other than that it's just a gamble. You won't explicitly have to adhere to EU standards, but you may lose access to the common market, very bad. And there's no guarantee that many nations wouldn't insist on similar terms during individual trade negotiations. So in the end you may end up saddled with a quiltwork of complicated or equally onerous regulations anyway. Who knows?