Mint, it's not a method I would use, but one thing I've learned this weekend is to trust your instincts when it comes to your own dog. I'm really pleased to hear he's improving and even spent some time lying peacefully outside when there were noises/distractions.
I managed to bag a last minute place on a training workshop with one of Britain's leading Lurcher experts this weekend. Had to get dh to drive me down to Bristol for 11.00 yesterday morning and spend the day in a sweltering riding school, but it was sooo worth it.
I learned a few handling tips, discovered what I have been doing is right - so cut through all the confusing/conflicting advice I've had re what to do when off-lead dogs fly up to us, was able to observe lots of canine communication, body language and calming signals in action and best of all have been really reassured about Pip and my handling of him in general.
He was clearly nervous and stressed when we arrived and walked into a hall with around 10 other hounds - but cautiously said hello to all the other dogs - excluding the couple that had aggression issues - and gradually settled down and relaxed - to the point he lay down and went to sleep later in the session.
The trainer asked us what we were there for specifically, so I told him about Pip barking at off-lead dogs and me not being sure of his intention or if I'm reading him right, that I needed guidance on what to do when an off-lead dog approaches my two uninvited and also that I was worried about him running off in panic towards the road if another dog tries to play with him when he's off-lead, as that's what he did a few times when he was younger. He showed us various handling techniques to keep control in those sorts of situations and explained really clearly why both dogs react the way they do.
Best of all he let Pip off in the school with another dog he'd never met before, so we could see how he reacted and observe his body language ... and he had a blast.
He and the other dog, a Saluki, were zooming around, taking in turns to chase each other, no hint of fear, aggression or any other issue and lovely clear, happy body language and communcation. It was lovely to watch and I am so reassured that he didn't just tuck his tail under and try to escape - he loved every minute.
Now I know I can let him off with appropriate/friendly dogs in the park, without worrying that he might try and run home and go deaf to recall through fear.
Then at the end the trainer very kindly came up to me and told me I should trust my instincts, because they're good, that Pip is doing really well and has lovely clear body language, so doesn't have a problem interacting with other dogs off-lead.
They're thinking of running a follow-up session in August and I've already registered my interest. 
It was a massive day for me, having not been further than the school and back and dog walks for months now and I was ridiculously nervous, but I am so glad I went. 