I'm a single parent and budget for everything, I literally write everything I spend in a spreadsheet. My biggest expense is also food. I like nice food, I rarely eat out but I cook a lot.
I reduced my food spend by opening a Starling account and transferring £500 a month into it. This covers food and the odd meal/sandwich out with DC. If it is heading towards the end of the month and the Starling balance is getting low we eat from the freezer.
Honestly, just that simple step on food budgeting makes a huge difference to my monthly spend. Before then I'd pop into M&S and emerge having spent £45 on one meal and not much else proper food wise.
Planning your meals and doing a weekly online shop will save you cash. I have a food delivery on Sundays and buy food for the week. I've had to change my thinking on shopping, for instance, if my DC decides to eat two yoghurts a day and they are gone on day 4 then they have to wait until the next delivery. Prior to going back to a food delivery I'd be popping to the shop. I don't top up the nice to haves mid week.
We both take lunch from home. DC is a permanently hungry teen so I'm happy spending £100-£120 ish a week on food.
We don't eat meat every day either which probably helps, two meat/fish free days a week. Tonight we ate this with a salad. Still probably cost £2.50 a head with nuts and parmesan but not the £5+ a head that eating fish or meat costs.
£1400, presumably this is before council tax, utilities, petrol, food and general life? It is easily blown if you don't keep tabs on it.
Don't cut out your lunch out each week, you deserve a bit of fun. Just make the saving elsewhere.
Get a freezer if you haven't already got one, it will save you money.
The mental burden of doing/paying for everything on your own and holding down a job that pays £50k+ a year isn't light and so you need to do everything you can to relieve stress. Organising your life to save cash and budgeting will really help you.
Get rid of the loan as soon as you can, I don't have any debt. I don't want the worry of paying for it/having my monthly available income reduced by it.