Green’s Dictionary of Slang

her indoors n.

one’s wife.

1981		A. Payne ‘You Need Hands’ Minder [TV script] 26: Specially if her indoors finds out what I spent on lunch.
1997		N. Barlay Curvy Lovebox 71: ’Er indoors might not approve.
1999		Indep. on Sun. 17 Oct. 27: No doubt it was her indoors, the Queen, who made him say it. But, no doubt, even Prince Philip will find forgiveness one day.