That is quite the eye-opener. They'd rather leech nursing talent from foreign countries, where the supplying country probably needs to retain that talent, than to do the morally right thing and invest in training.
That said, expecting someone else to have trained potential staff and being able to pick from the resulting resource desperate for a job, seem to be the modern company ethos these days. Possibly because staff are not valued and the company has a duty to look after them, but rather they are a commodity resource that one gets and dispenses with, as if they were desks or chairs or PCs. They're there just to be used as required.
What is the problem here ? Are they worried they will spend a fortune on training for those trained to go get better paid jobs elsewhere ? In which case raise the eventual post-trained salaries to the market level, and add a pay-back clause if someone wishes to leave before x years after being trained.
No one seems to care, or want to do the right thing. There should be laws to ensure immigrant labour is only allowed if posts are unfillable from those citizens already here, and are not offering UK pittance level wages to ensure no national interest, but that reward/environment meets UK expected standard.
If Brits won't do a job then it seems likely the reward for doing it is not attractive to UK citizens. It's the market in action. If there is low demand then the employer needs to allocate more financial resource, or other attraction, to the position, to increase the demand for the post. But apparently the labour market isn't allowed to be affected by supply & demand, potential employers are allowed to short circuit the system by looking outside the UK market for those more desperate or with lower costs/expectations.