Nigella's one (well, they're called Lily's scones so she must've pinched it from her!) is foolproof and yumtious:
500g plain flour
1 tsp salt
2 tsp bicarb of soda
4.5 tsp cream of tartar
50g cold unsalted butter, diced
25g Trex, in teaspooned lumps (I think this is a bit wanky meself and just hack it out of the block before dicing) or use another 25g of butter, or do what I did when short of both and use lard (if you're not a veggie) - it worked great!
300ml milk
1 egg, beaten (optional)
Preaheat oven to 220c/Gas 7
Sift flour, salt, bicarb, c of t into a large bowl. Rub in the fats until it goes like damp sand. Add milk all at once, mix briefly and turf the soggy lump onto a floured surface before kneading to form a dough (messy!).
Roll out to a 2cm thickness, you get 12-13 scones from this but may need to reroll a few times.
Put on a greased baking tray and brush the tops with beaten egg if using. Cook for 10 mins until risen & golden.
Make fruit scones by adding 75g of sultanas/raisins/whatever you want, make cheese scones by adding 75g grated cheese.
Lush!