A programme theory for liaison mental health services in England. - House, Allan; Guthrie, Elspeth; Hewsion, Jenny; Brennan, Cathy; Murray, Carolyn Czoski; Walker, Andrew; Trigwell, Peter; Crawford, Mike; Fossey, Matt; Hulme, Claire; Martin, Adam; Tubeuf, Sandy; et al. (BMC Health Services Research, 2018)