If you're not familiar with it, bangers and mash is a game of two halves: mashed potatoes (the mash - you guessed that, right?) and sausages (the bangers). Traditionally most people would be eating crappy meat sausages, which is where the bangers name come from - when they were cooked, they'd pop apart with a bang.
So traditionally bangers and mash are made with crappy meat, but we have a couple of good vegan sausages - there's Redwood's and Linda McCartney, which you can find in most supermarkets in England, and the latter are the ones I've used here.
When I was a kid, bangers and mash were fairly standard dinner. Along with the sausages and occasionally lumpy spuds, you'd get peas, and gravy out of a packet if you were lucky, and proper onion gravy if you were really, really lucky.
Gravy is one of those concepts that the UK views differently to the US - it's like whether football should be a sport mostly played with the feet, and the importance of dentistry. Gravy over here is basically thickened stock, usually poured over a roast dinner. There's definitely no biscuits involved (unless you have something to dunk in your tea afterwards).
Proper onion gravy is the sauce bangers and mash deserves, and it's as time consuming as bangers and mash is easy. You sweat two finely sliced up red onions with a pinch or two of sugar until they're all caramelised - a matter of half an hour or so - then stir in some flour, and cook it out for a minutes or two. Then add some vegetable stock, a little red wine vinegar (or cut straight to the chase and get red wine itself involved), some woody herbs (any of thyme, sage, rosemary is good shiz) and mustard and let it all cook down until good and thick.
Then drown your sausages and mash in it, and face plant yourself in.