Dear AnnaStrophic, the phrase comes from a long gone but deservedly popular British TV programme called The Minder. George Cole portrayed Arthur Daley, a second-hand car dealer cum general minor rogue with a wife who was never shown. He always referred to her as " 'er indoors".
Dennis Waterman (who had previously played 2IC to John Thaw in The Sweeney) played the part of the eponymous minder (ie: bodyguard) to George Cole. It would be oversimplifying things to consider the programme as just another comedy. George Cole, an excellent actor - I first remember him in 'A life of Bliss' on the radio - became well known when he took the part of Flash Harry, the spiv in the St Trinian films. He is that type of character actor who always gives good value for money and is capable of holding a play or show together and lifting everyone elses performance. Although he has usually played in comedy he is capable of putting a lot of depth into his work and really developing a character. I have seen him play villains and romantic leads with total assurance. His development of Arthur Daley as a likeable but selfish coward from whom you were always hoping for better things, but never getting them, was masterly.