Hello everyone, thank you for all your considered responses - I do really appreciate them.
To clarify a few things: my dog does NOT approach other dogs, so we're never in a position where we're up close to another dog. The attackers go out of their way to come to us, which is what is so odd.
I've done a LOT of research on dog body language, and am constantly scanning the horizon when we're out, so we avoid dodgy situations most of the time. These attacks are those very rare ones in that there is literally no warning, no body language, nothing. So weird.
She's white (someone asked if she was black), but quite unusual in terms of her breed. Perhaps that's triggering in some way? The first few attacks, the owner of the other dog tried to blame it on the way my dog looked... which felt daft at the time but as there was no warning, there could be something in it.
I have looked into sprays. The noisy ones would deffo traumatise my girl, so they're out. The 'smelly' harmless ones seem better and I have ordered one. I have also read up and watched some videos on how I can place my body between her and the attacker, and effectively block the attacker. And use my Big Momma voice, and shout NO. (I did actually use this on some French dogs that chased me years ago when I was running in Cannes (without my own dog), it worked a treat. I did however change it to 'Non' so that they'd understand better!!).
Throwing a handful of treats at the attacker can also work, apparently. I almost always have treats in my hand as I'm constantly training my girl, so it's easy to do.
I have also booked a session with a behaviourist to teach my dog to run between my legs when attacked or threatened. She is also going to teach her to play with other dogs: she is avoidant (and the attacks really don't help with that!), so this could perhaps be triggering the attacks also.
And we're doing all the things suggested, like varying our runs and so on. It is pretty much impossible to avoid other dogs given where we live - god, how much would we love to live in open country, or in places with quiet parks. Everywhere we go is packed to the gills with furries. But I'm doing my best.
I'm very reluctant to put her on a lead, as I think this is the wrong approach. Given that she is NOT going up to other dogs (they're running at her), then her being on a lead will not help and may put her at a disadvantage, as in, she won't be able to get away. So I am focusing on getting her to come to me instead when threatened.
I'd love to hit the attackers with sticks, boots, fingers up bum and so on, but honestly? Everything I have read says that won't work and may well make things much worse.
The RSPCA says to report to the dog warden. We have no dog warden. The council says report to the police. The police say they can't do anything. I have film, photos and registration numbers but that's apparently not enough for anyone at all to take action. This is the bigger and more worrying picture: I do fear that the explosion in lockdown dogs, untrained, with clueless owners, and with no recourse to any sort of legislation, is going to lead to an escalation in attacks. But no one wants to hear that, at a civic or legal level.
Anyway, I wanted to thank everyone for their advice. I have listened, I am taking action. And I really wish you all safe and happy walks with your lovely and clearly well behaved dogs!