When it comes to bangers and mash, a good wine pairing is a classic English ale.  A malt-forward ESB (Extra Special Bitter) or a well-balanced Pale Ale are both great choices. They will bring out the caramelized notes of the sausages without overpowering them.  For added depth, a fruity red like Pinot Noir can be an excellent accompaniment. It will cut through the richness of the dish while still providing an enjoyable sweet and fruity flavor.  As far as whites go, look for something medium-bodied, such as Chenin Blanc or a Sauvignon Blanc with herbal aromas that will create an interesting contrast with the mashed potatoes and sausages.