My business costs last financial year were around £7k
£7k sounds surprisingly low, but the actual figure is irrelevant.Of course, the business also paid your pension contributions, your holiday pay, your sick pay, and your professional registrations.
Whether they be £7k per year or £70k per year, your 'fixed overheads' should be included (by assuming a certain number of hours' work per year0 in the notional 'hourly rate' which you use as the basis (before adding on job-specific expenses) for calculating the total to quote to/charge a customer for a particular job.
Those fixed overheads ought to be pretty similar regardless of what part of the country you are in - the only appreciable variation I can think of being in relation to vehicle insurance.
Kind Reegards, John