I've just trawled through a typical month of bank transactions.
House (tax, energy, water, phone/BB/mobiles, insurance) - £820
Shopping (food, coffees, consumables - no clothes, tools etc etc) - £800
Petrol - £124
So that's £1744 gone.
Apart from petrol there's nothing in there for car insurance, maintenance....or purchase. Nothing for clothes, TV licence, streaming etc or towards stuff for the house, I've ignored Amazon, Screwfix outgoings that month and optionals like Spotify and dental insurance). If you haven't got a decent kitty you'll need to save towards stuff like cars, bicycles, house repairs, decorating, holidays. (Knee replacements? ).
Sure, two can live on less than £3k a month, but I wouldn't want to.