It's more important that you have the savings, rather than the amount is exactly right or split up into pots for specifics.
I like Ohios designations - 'expect to use' would cover MOT, insurance, Christmas, holidays, appliance repair/replacement, school uniforms etc, so you will probably need to put a few hundred pounds a month away for these things. I think that's where a lot of people's budgeting comes unstuck - they don't realise how much all these irregular but expected expenses add up to and don't put enough away and then look at the money they have after bills and think 'I have loads of money for eating out, clothes, lunches, days out, gadgets etc etc' when in reality, they don't.
Almost never touch would be loss of income, maybe major repairs, house moving? and never touch would probably be pensions?
Somewhere within the moneysavingexpert budgeting section, there's a comprehensive list of expenses that you can work through and identify the ones that apply to you, whether you have DC, pets, own or rent, have certain hobbies and interests, run a car, like to spend a lot on holidays, etc etc
www.moneysavingexpert.com/banking/Budget-planning/#bplanner