According to the BPS "Occupational psychologists are concerned with the performance of people at work and in training, how organisations function and how individuals and small groups behave at work. The term 'organisation' is used to describe a group of people working together with a common purpose or goal."

There are a number of 1 year full-time and 2-year part-time Masters courses across the UK at some 23 institutions.

You can find the Division of Occupational Psychologists here.

Recommended reading:

Psychology at Work ~ Peter Warr (Editor)

The Psychology of Behaviour at Work ~ Adrian Furnham

Neuropsychology for Occupational Therapists

Introduction to Industrial/organizational Psychology ~Ronald E. Riggio

Personnel Psychology & Human Resource Management ~Cary L. Cooper, Ivan Robertson