First, for the haggis: Bring a largeish saucepan of water to the boil. Place the haggis in the pan and lower the heat so that the water simmers gently - you don't want the haggis to burst! Wrapping your haggis in foil can help prevent this. For a 1kg / 2lb haggis, you'll simmer for a good 75 to 90 minutes, but ask your butcher for best results.
Meanwhile, peel your neeps and tatties. Cube them, then boil separately till tender (I start this about half an hour before my haggis is finished). Drain, then mash separately with a good bit of butter. If you like, add a glug of milk to get a smoother consistency. Then add salt and pepper to taste.
Once your haggis is ready, serve alongside the neeps and tatties for a traditional Burns supper.