https://www.theguardian.com/society/2016/dec/18/nhs-doctors-locums-pay-finance-hospitals

https://www.theguardian.com/society/2016/feb/11/are-locum-doctors-and-nurses-really-bankrupting-the-...

One answer could be that, instead of getting locums from outside private agencies; each Hospital runs it's own staff bank.  Staff called in, are paid a reasonable overtime rate; time and a half or double time. If a Doctor was on £20 per hour ( and trust me they're not........unless they've been at it for quite a few years ) that would be a max. of £40 per hour..........NOT £100 per hour and there'd be no agency fees.