Import the ingredients
Well, for starters get decent bread. Anything that is pre-sliced and on supermarket shelves is shit. Every single one. You can thank the Chorleywood bread process and Britons' obsession with price over quality for the part-cooked, spongy muck that passes as bread in the UK. Bleurgh.
So either get something decent from a local baker (a real one, not the one at the back of the supermarket. I said a real one, not Greggs either) or import some toasting bread (Germans do good stuff, French/Dutch can often be too sweet, Ciabatta can be good as well). Wholemeal with seeds/nuts is great for texture and added bite. Just avoid ANYTHING from the likes of Hovis etc.
Next cheese...forget the cheese aisle. Block-upon-block of tasteless gunk passed off as (usually) cheddar. Bleurgh again. Price beats quality in the UK once more and you lot seem happy with your single cheese choice of "Mild Cheddar" (a bit like you beer choices of "Shit American Lager" or "Shit Fake French Lager"). Seriously...the UK used to have decent food, not any more and it make you a laughing-stock.
So go to a local cheese shop (once again, ignore the counter at the back of the supermarket) and buy some decent hard cheese. It'll probably be imported, unless you are really lucky and can actually get proper Cheddar (which tastes nothing like the crap Tesco et al sell - to be honest, most of their "cheese" should fail under the Trade Descriptions Act!).
Toast yer bread (I like to leave one side just slightly under done).
To the under done side, add cheese slices.
A dash of Worcestershire sauce OR crumble on some strong Stilton (about the only British ingredients)
And then toast under the grill using a high-ish heat.
You are looking for the cheese to start bubbling, but the bread to not become a charred cinder.
Allow to cool slightly (use a cake rake or the underside will go soggy)