£600pcm mortgage
Bills must be another what £200 pcm - internet £20, mobiles X2 £20, gas and electric £60 minimum ?, Council tax £100 minimum, water £20 minimum, and then annualised house insurance - realistically this will be more like £250-£300 (so £900 running total) - and that excludes anything like netflix etc.
Running a car - insurance must be £200 a year, car tax often £100-£150, MOT and service - another £200-£250 minimum - there's no way this is less than £600 a year, I usually count mine as £1200 for safety. (Running total say £1000)
Petrol - £50 a month minimum presumably for petrol? Lots of people will spend £50 a week if they have a commute. (RT £1050)
Food - not likely to be less than £50 a week with a family surely? (RT £1250?)
That ignores anything like: season tickets, gym membership, haircuts, presents, clothes, children's clubs, annual things like Christmas which need to be divided by twelve and saved for monthly, any childcare costs you might have during a notice period, anything like professional membership fees if you have to pay them (mine are £400 a year so an extra £30 a month), the cost of saving up for a new phone over time or the additional cost of a contract which includes a phone, the cost of saving up for your next new car, anything like a more expensive internet connection, netflix subscriptions etc. You might not have any of these, but if you do have them they might not all be able to be cancelled with no notice so you have to account for the cost.