When starting a new job, an employee must present an employer with their P45 to show their earnings to date so that the correct tax can be calculated. If they have two jobs or more, they get multiple tax coding notices to hand to their multiple employers. Employers must maintain complex arrangements for dealing with tax coding, as do HMRC.
HMRC must employ countless staff to deal with tax coding management and enquiries alone. HMRC have to maintain software to cope with the changes to this system each year and track the multiple jobs.
The answer is to extend the simplifications to the benefits system further, and instead of a plan for a £12,500 personal tax, make it zero
and introduce a Citizen's Dividend of £2,500. All benefits would be reduced by £2500/yr to match. (The figure could be higher if we did the
same thing for national insurance contributions, but that could be left as a rainy day policy for the future).