Totally agree with Chloe - kibble 2 X 40g with a sprinkle of green beans and nothing else a day, with at least 1/2 hours fast walking should do the trick.
Gravy bones - for a small dog should be max 5 per day according to their instructions on a kilo bag.
My two get 4 gravy bones for breakfast, 100g of Burns with 1 natures menu banquet nugget on top and a 1/2 a charcoal bone for supper. They have 2 x 30 mins excersise a day Mon- Fri and then at least 1 hour walk/play/agility on weekend days and they are superfit and superlean
I'm afraid you have to be harsh, if you dog does not burn off what goes in, rather than cut what goes in as much, get more out of your dog - why not join an agility club - we burned loads of calories last week - even on our 1st pre agility lesson
Best of luck anyways