I’m not in the same situation financially as OP, but we have needed to cut back due to other costs increasing significantly. These might not be applicable to you, but thought I’d mention them anyway!
i’m also letting my hair grow out - and have stopped the 6-8 weekly hair dresser trip. I actually get my dh (aided by my 12 yo dd!) to trim my ends a couple of times a year! We have proper hair cutting scissors (as I tended to do family hair) - and I explain very clearly how to do it, while they are doing it. I section it up with clips and they follow my instructions… it works well as my hair has got much longer and is one length and very wavy, so it doesn’t need to be perfect! I home dye with semi-permanent dyes (it can almost look like highlights if you have greys, and it grows out much less obviously) - look out for special offers on multi-buys.
I have massively reduced my expenditure in boots / Superdrug for toiletries.. i made a resolution to use up everything I have already, so it is also acting to de-clutter bathroom cabinets as well. I no longer buy special moisturiser / cleanser for myself, I have actually found that using any type of cream / moisturiser / body butter can be used as a facial wash (this may not work for some people who have very sensitive skin), so am using up all of the random gift sets that I have received over the years. I also use bar soap (but tend to go for the Dettol one).
I am doing the same in the kitchen cupboards and freezer - usually my food cupboards have random residual packets / tins of stuff in, so am making sure to plan meals round what there is (sometimes these are a bit random combinations!) and have been avoiding going to the shops unless I actually need fresh things in.
One question I would ask, @Moneyschploney , is are your dc fully aware of the situation, and are they also making efforts to reduce spending / save money? I only ask as I have a friend with teenage dc, and they have financial problems, but my friend seems to have a blind spot when it comes to the dc - they are still having quite a lot of money spent on them, and still have quite expensive tastes (teen had nails done (£40) before Christmas, and the mum paid for it as she didn’t want her dd to feel left out, amongst her friend group). If teen dcs are able to work, then they can start to pay for more of their own things (if they are old enough).
With my dc at school, lunches can be a big area to save money.. in the canteen it can be up to £5 per day - and they like to do that to be social with friends.. but that works out at up to £200 per month. Packed lunches can be much cheaper.
Re; having half a tin of soup as a main meal - that can work really well, if you can add in some other things to bulk it up / add nutrition. I add a handful of cooked plain pasta (from a box in the fridge, it keeps for a few days) to tinned soup, and also bags of frozen chopped spinach are great, you can bring in one or two cubes to the saucepan when heating it all up (fresh tomatoes also work well, with the spinach, if you ca manage that). Also adding in chickpeas. Plus can always put more spices / seasoning in to add flavour.
Buying fruits / veg frozen can be a good / cheap way of getting veg in. I go for bags of chopped onion and bags of chopped peppers, as you can use just a handful.
Lidl is brilliant for shopping. And switching out the most expensive items for cheaper alternatives works well (so if your dc are big cereal consumers, switch to Lidl 85p versions rather than £3.25 branded versions, or switch to Lidl porridge oats - even cheaper).