Do you cook from scratch, or use jars, or just "ding dinners"?
If you can cook even a few things from scratch, you will save a lot.
So make a basic spag bol sauce - but do enough for 2 or 3 dinners. Eat 1 dinner, freeze a second to make a lasagna (could even freeze that already made up, to just bake when defrosted), and a 3rd could either be another night of spag bol from freezer or the base of a cottage pie with mashed potato on top (which could be leftover from the previous night's steak/lamb chops dinner - just peel an extra 3 potatoes or however many you need for the pie).
Lots of curries freeze really well, cook well in big batches, and work best if you make the sauce and leave it slowly simmering for a good while - so ideal while you are still on mat leave to start in the morning/at lunch, turn off after a couple of hours simmering and just reheat in the evening when DH gets in and cook rice fresh.
Do make sure you have plenty of vegetables in dinners, not just meat. In "saucy" dinners, I have lots of mixed veg added - both for nutrition and to stretch out the meat. And there are loads of lovely dinners that are veggie - we try to have either a veggie dinner or fish rather than meat at least once a week.
Check your brands too - some things do seem different but lots don't really matter. So I tend to use "better" brands for things like jars of sauces (for when I don't have time to cook from scratch) but then use value or basics easicook rice as I can't see any great difference.
Online shopping can help keep costs down by not grabbing things as you pass. But start with a list of what you plan to eat next week rather than "oh I fancy that". And check the cupboards before you start too (I have a habit of buying apples, or tinned sweetcorn - and having loads still to use at home!).
Maybe, if DH does the shopping but it is an online shop, you could do it together in the evening for a few weeks, or you can take over temporarily and get a chance to change the "usuals" that come up to things that better suit your current needs and circumstances.
In our house, we have DH and I both working FT, and a 10yr old with fussy tastes (ASD so there is a certain amount of pandering to it so she will eat - she is on the 4th centile for weight). So we have a reasonable amount of convenience foods, and some alcohol, lots of fresh fruit and veggies, lunches for at least 2 daily, all meat eaters, etc but we are gone beyond formula/nappies. For us, and we feel like we spend a lot, it is roughly €150/week (about £120) - you should be able to reduce your spending a LOT. And we have a mix of M&S and the local equivalent of Sainsbury's.