I've started to use Lidl and it really has cut my food budget. To be honest, the range is limited, so I go to Lidl on the way to Safeway (they're only few hundred metres apart), get what I can there and then finish off my shop at Safeway.
The sort of things a get from Lidl are cheese (a big slab of Emmentalle for a silly price), E.V. olive oil, tomatoes, bacon, jam, mini-juices for ds, vegetables, cheap crisps for ds... They're also good for some luxury items, like 70% Chocolate (good for baking!), or Jaffa cake subisituites that are better than Jaffa cakes!
I'm still quite snobby about some things, like Kellogs Cornflakes (for dh) and I need Safeway for more specific items, eg almonds, spices, little fromage frais for ds.
I've also found that doing a menu for the following week and then making the list has really reduced my weekly spend.
I was even able to "splash out" on a BBQ at Lidle last week - a whole £10!