I bought Harvey (15.2hh Hanovarian x Cob) at the end of April 2012, and he was very overweight. The owner wanted to sell him as she didn't have the time that he needed or as she said "deserved". B&W Equine Vets recommended I started Harvey on Shape Up and Slim Chaff, and for the first 6 weeks just ride him in walk, in school and on hacks, gradually introducing trot work.
Harv May 2012
Saracen SW Area Manager Nikki McGee came to my yard and assessed Harvey's paddock, and gave me a feed plan. Nikki recommended to either put a muzzle on Harvey, or strip graze so he would not have too much grass, and bring him in the evening. Emphasis was paid on feeding small amounts of hay, little and often. Ideally, Nikki recommended feed morning, afternoon, and evening, and weighing how much hay I gave him. Unfortunately, due to being at work I was unable to do this, so would feed him in the morning and evening. Harvey did not take to a muzzle very well at all, so I decided to strip graze his paddock.
Nikki introduced me to Shape-Up as I needed to feed a balanced diet, but not provide too many calories. Shape Up is a Balancer, so you feed small amounts to provide the balanced diet. What I liked about Shape Up was that it is a mix, so I still feel like I am giving Harvey a feed, but I know it is low in calories. It smelt fantastic which I learnt is due to an inclusion of Cinnamon which is known for its positive affect on the metabolic system.  
In August 2012, I moved Harvey to my friend Pauline Martin's yard. She was instrumental in helping continuing to bring his weight down. I focused mainly on trotting and cantering a lot in the school, doing this 2 or 3 times a week. Pauline would ride Harvey once a week, alternating between schooling and hacks and his feed and hay was weighed and would be adjusted according to how much work he did.  
Due to work commitments I was unable to ride as often I would have liked to, so he was on Full Livery from December 2012 until January 2013, where he was ridden 4/ 5 times a week, which included being ridden in school or out on hacks by Pauline, or by her yard assistant Jade Marie. I do believe the regular exercise whilst on Full Livery was key in bringing his weight down, also the cold winter contributed to a degree. 
From February 2013 he was back on Part Livery, so I now try to ensure he is ridden at least 4 times a week, either in school and occasionally on hacks, to try to maintain him at the correct body condition. 
Here is a pic of Harvey now - I am so thrilled with the results, I have a happy, healthy pony, and am so grateful to everyone who helped us achieve this significant weight loss.