I'm Aussie so wouldn't have a clue what a real English breakfast is supposed to comprise of or taste like. but my understanding is that you need the right type of ingredients, eg. the sausage and bacon need to taste a certain way (Cumberland is the best?). which makes it a kind of niche product and therefore best handled by specialist restaurants.
my go-to when I'm in Patts is the Sportsman on Soi 13. but last time I was there in Feb the pork sausage was a bit ordinary. more like an Aussie banger than a Pommy one ????