Thanks again everyone for your comments.
We had a great day at the beach at the weekend. Baxter's recall was perfect and we allowed him brief encounters with other dogs. As they were quick meetings, they were all positive, lots of wagging, quick sniff then we called him back and continued walking.
We didn't stand talking to anyone, so there was no opportunity for boredom leading to pawing and snarling.
At the park, I have kept him in wide open spaces for exercise and then on lead as we pass other dogs on lead. He is more or less ignoring other dogs as we pass them and we have had no outbursts for 3 days or so.
If we can continue with lots of positive outings, it makes sense to me that he doesn't form the habit of always interacting agressively.
I will be following your advice and hoping for our little lad to be a happy chap again
