Things I've started recently to cut costs:
Buying a lot of meat and fish in the reduced shelf in Asda - I get a lot half price when the date is up and freeze it. Its great for things like pies and fish that can be cooked from frozen.
Using pulses more - I cook in bulk, so a tin of lentils in a batch of lasagne stretches it further, 5 lasagnes instead of 4 etc
Buy rice/pasta etc in bulk - Asda do 3 kg bags
I am fickle with my shopping - one week I shop at Aldi, one week it is Ocado (I get everything on offer, half price usually, so it works out cheap), one week in Asda etc. I meal plan about a month ahead, so I buy things from wherever they are cheapest.
Using frozen veg and herbs - it saves a huge amount of waste.
Making all our bread in the breadmaker - we make what we need instead of eating it just to use it up.
Cook meals in bulk and freeze - loads of things freeze really well and its lovely not to have to cook from scratch every day. Also, something like chorizo works out fairly cheap if it is going in 3 meals, the taste is still there.
Definitely agree with people who suggested dishing up smaller portions, especially with kids. Some days they eat seconds and thirds, other days they hardly eat anything. Anything leftover can be used again.
And a biggie - grow your own if you can - you'll save lots on salads and herbs and if you have room try growing soft fruit - if you can beg things like runners off raspberries etc you can do it for next to nothing.
My budget is £70 for me, DH, D1 (4yo) and DD2 (18m), including nappies, cleaning products etc. We could cut it further if we cut out the more expensive ingredients like chorizo, but we don't need to at the mo.