Thank you for all your kind responses.
An update: my dog has made a full recovery and is enjoying the park once more.
I haven't found the owner however thanks to NVN so many people have read this post that I am hoping it has been seen by her or someone who knows her, assuming she is local.
I have discovered an amazing charity called Yellow Dog www.yellowdoguk.co.uk
where your dog can wear a yellow bandana or muzzle to show other owners that their dog needs some space. This looks to me like a brilliant scheme - and could give a dog owner more peace of mind when taking a nervous or potentially aggressive dog out in the park and they don't want other dogs or children to approach their dog - or approach with caution. This helps everyone and can conceivably prevent an encounter that could easily end in the death of a dog or an attack on a child.