Back away from the wooster sauce, ketchup & bread crumbs, your not making meat loaf.
I have a food truck, and do burgers, hand cut fries & beer battered onion rings. I also cook all my burgers on a char broiler.
80/20 ground chuck. Fresh, not frozen. Seasoned only when it hits the grill, I make a seasoned salt with granulated garlic & onion, pepper & smoked paprika.
Don't know what is common for burger buns across the pond, weather your selling a $5 burger or a $15 burger. Buns can range from plain crappy white bread, your standard seeded bun to brioche.
A good quality American cheese is a must, you can offer others, but this is my default, it melts well and is not oily like a cheddar. I also offer cheddar, swiss, provolone, pepper jack & crumbled blue.
A well toasted bun is a must. I make a spread (1000 island) that goes on most of my burgers.
I use heavy mayo, ketchup, sweet pickle relish, grated onion, granulated onion, salt, pepper & a bit of dill pickle juice. Must be made in advance, needs 24 hrs for the flavors to marry.
So a basic burger goes on a well toasted bun, good amount of spread on both sides, squirt of mustard on the top bun along with a good amount of paper thin sliced onion, on the bottom bun 8-10 dill pickle slices, nice slice of tomato & shredded iceburg lettuce.
There is a million ways to skin a cat, that's my method. My clientele is looking for a $10 lunch.