We have a 15 month cocker who went through a phase of eating his poo whenn he was a puppy. we thought we'd conquered this, but lately I Have my suspicions that hes doing it again. This is not happening all the the time but I dont trust leaving him now when he's been to the toilet. We took the dog to the vets for a routine check up recently and he said the dog was overweight so we reduced his diet. Is this linked? if so how do we stop this habit and at the same time keep him at the right weight.I would be grateful for any other advice. Thank you.    

He may be eating it for many reasons however the following are some things that may help:

Diet - make sure that he is not eating too much, this will just go through the system quicker and much will remain undigested and therefore attractive to the dog.  Ensure the diet does not contain too much cereal consider Burns for dry or Naturediet for moist, these diets tend to be well absorbed by dogs even though the do contain rice.

Think about adding Digestive enzymes to the diet particularly bromelain, papain available from any health food shop, these breakdown the diet further.

There are products that you can buy from the pet shop such as Deter which make the poop taste disgusting or pineapple or courgettes in the diet may help some dogs due partly to the enzymes and partly to the taste these may impart to the dog.

If the dog is very hungry, consider offering whole raw carrots, broccoli, etc to fill up the gaps, satisfy the hunger etc.

Yes it is linked, he will be feeling hungry as he is on a diet and looking for other sources of food, unpalateable as the thought it, faces haqve still a lot of nutritional valuye, so many dogs on restricted food intake will indulge in this.

The only thing you can do is ensure that his toilet is cleared up right away.

As for assuaging the dogs hunger pangs you can give him vegetables like runner beans, unwsweethehd tinned pumpkin (popular in the USA) Carrots, and Cabbage to bulk out his meals.  It will give more voluminous stools, but should help with the problem.