From looking through past forum posts, it looks like you can, to a certain extent, choose. And you can make your own up. This indicates they don’t matter beyond helping me, the business owner, know what’s been spent in which area.
For example, I use Sage for payroll. Different posts suggest I should use “Licences (7302)”, “Subscriptions (8201)”, or that I should create new one called Software. Does it matter which one I use? Why?
In the main the nominal codes are for your use, to help you understand where you are spending money in your business. To this extent you can adapt the chart of accounts to suit your particular circumstances and add or change existing codes. However, there are certain account codes which are set and used for specific purposes - such as salaries, fixed asset and depreciation codes, for instance, or accounts payable/receivable.
There are also some expenses which you need to make sure you keep separate as they are not allowed as tax-deductible - you will need to be able to identify them separately when you/your accountant come to do your tax return. These are things like (again) depreciation and business entertaining to name the most obvious ones.
For smaller businesses, HMRC allow you to report total expenses without requiring a breakdown, but it is necessary for VAT-registered businesses and so the expenses should reflect the headings appearing in the tax return.