Mindfulness Based Cognitive Therapy is a standardised MBI that is a recommended therapy by the NHS (NICE Guidance CG90) for the prevention of relapse in depression. The NICE guidance recommends "Mindfulness-based cognitive therapy should normally be delivered in groups of 8 to 15 participants and consist of weekly 2-hour meetings over 8 weeks and four follow-up sessions in the 12 months after the end of treatment. "

MBCT is derived from
MBSR, and there is significant overlap. They key difference is around emphasis on low mood and negative thoughts (See http://www.umassmed.edu/cfm/mbct/mbct-and-mbsr-differences/).

MBCT has been the subject of a number of controlled clinical trials that demonstrate its efficacy. (For example, see
The Lancet)