It could be from the plaque on his teeth? If it is then either vet for teeth cleaning - or I give mine big raw knuckle bones to chew on - which helps keep his teeth clean (But that's personal choice - you might prefer not to do that.)
But if there is another veterinary reason for the bad breath - then maybe a trip to the vets would be best first - to make sure you know what is causing the problem?
Thank you. Ive got an appointment at 5.30pm tonight. He's got lovely white teeth, so they said it may be a bad tooth or gums. Will report back tomorrow.