NHS pays £20,000 a week for a doctor

[ikri]

2. Or, more realistically

Hospitals are paying agencies to hire locum doctors to cover gaps in care. Agency rates are known to be exceptionally high (agency nurses can earn more than a regular nurse but with no guarantees about where or how often they'll work) but they're useful at filling holes in planning. The doctors won't be earning £20k per week, they'll probably earn a higher hourly rate than the equivalent permanent staff member, the rest will go to the agency employing them.

If they want to avoid paying temporary staff huge sums they need to hire more permanent staff to fill those gaps.