Green’s Dictionary of Slang

partake of His/Her Majesty’s hospitality v.

to spend time in prison.

1894		Strand Mag. Sept. 296/2: Partaking of Her Majesty’s hospitality, in a building specially erected for gentlemen who need a compulsory holiday.
1938		F.D. Sharpe Sharpe of Flying Squad 157: One awful thug I know, who is now enjoying His Majesty’s hospitality, beat his woman up regularly.