Your post made me curious, there are 301,000 nurses in Englang.brexit too - I did present my remainer priority pass when I attended A&E
Record number of NHS doctors and nurses in England
Provisional figures show that as of January 2021, there are a total of 123,813 doctors and 301,491 nurses working in the NHS.
www.gov.uk
So those 5000, account for just under 2% of the nurses in Englang.
Now we don't know where these nurses work or the breakdown through out the NHS. So while brexit didn't help its most likely not the issue here.