Cottage Pie: Essentials Mince 500g (fry off the fat, actually much tastier), tin toms (essentials/basics), an onion (if your dd will eat - not essential), handful of mushrooms, carrots, cup of made-up bisto gravy, potatoes - probably about 500 - 750 g.
fry off mince, you can soften the onion and sliced carrots in the tomatoes (if you can't stretch to a bottle of oil), add mince to onions, chuck in chopped mushrooms, let it simmer a bit, add the gravy (bisto will do - two heaped tsps to a teacup), if you can stretch to a bit of brown sauce or lea and perrins it will add flavour. Put in a deepish dish and let it cool overnight. Next day boil potatoes, mash with a bit of milk and butter if you have it. spread over the mince mixture and bung in a hot oven for about 35 minutes.
That can probably be done for about £2.50 and if there are just the two of you should do three portions each.
Fish pie: white fish (cheap stuff such as coley is fine - about 400g), some smoked fish (200g) or a tin of pink salmon (on special for £1.50 at the Mo), poach it in about 3/4 pint of milk for about 6 minutes. strain the fish and keep the milk - strain into a jug. 1oz butter in a saucepan, one level tbs plain flour in the melted butter. Give it a good stir, add the milk, stirring all the time until it thickens a bit. Add some salt and pepper and some fresh parsley if you can stretch to it. Fold in the fish and allow to cool. You might want to slice two hard boiled eggs onto the top if you like the sound of it. Let it cool overnight and then pop the mash on as above and bung in the over for 35 minutes. Again this should do 3-4 adult servings and 3-4 baby servings.
Serve both the above with a green veg.
I live in London too - can you get to a market for cheap veg?