Joyce is what is technically known to the Scottish medical fraternity as "aff his tattie".
Exhibit A.
After 4 yrs in the ranks in the Black Watch he went off to Uni and was commissioned in the RAEC. He left the Army in a hissy fit as a passed-over Major spouting about racism and walked into a sinecure with the CRE before landing a safe Labour seat.
Given that he was the top claiming MP and the first to pass the cumulative £1M mark, many have been hoping he wouldn't let the door slap his backside on the way out for some time. I suspect this is an engineered departure with a rather confused veneer of 'principle' tacked on.