This is quite a random one but in my quest to slow my dog down when approaching other dogs I have had some slightly random thoughts.

To give you a background, I have been working on how my dog greets other dogs for the last couple of years. He always charges up to them at full pelt and being a Lurcher this means it's pretty fast. He does this even when they're only a couple of meters away which is a bit unerving for both the dog and owner.

I've done all sorts of classes and training things but he still doesn't know how to slow down his approach as he seems to only have two settings, walk or run reeeeeeeeeeally fast!
I actually have no idea how to solve it now because it's not even a recall thing because he does it when meeting a dog close up when he's next to me! I guess most people would address this at puppy stage but I got him as a rescue when he was 5!

When I got him he didn't know how to sit until I taught him, now he sits for anything, it almost seems to be his favourite postition so I thought maybe if I could teach him how to do a canter (which most dogs do naturally) that maybe he would start incorporating this into his general movement repertoire.

I know this sounds a bit weird but if anyone with training experience could advise or even suggest something more sensible, I would really appreciate it.
FYI I also do off lead socialisation classes at which he never displays this behaviour but then he's quite aloof whilst he's there. Problem is he hasn't generalised what he has learnt there to use in different places.

It is recall or it isn't

That question stuck into my head long time ago. If your dog is faster than yours words what then?
I have lurcher and the same problem. She will run like the wind, stops few meters away from a dog and comes back really happy. Or if a dog is moving away she will wait for good distance to run, and run to him...
I promised myself next time I will take the slowest dog on the earth
Did I mentioned that I love greyhounds?

I don't know how to stop that fast dog. Maybe you can't and better will be to socialize him to hight standards with many, many dogs? If your dog won't fight and is enough fast to run away from it, plus he has got good recall there is nothing to worry of.
When he runs towards another dog how he behave? How good he is with calming signals? Is he can read them and adjusts his behaviour too them? If Halle runs towards a dog, a dog stand/sit still she will stop and sniffs the ground. This take a place even if owner will stand between them, so she will "calm" the owner
If your dog isn't aggressive towards other I wouldn't worry too much. Keep him away from roads and he should be fine.

I have also thought I'd get a slower dog next time lol! He socialises with dogs every day. I have a dog walker so he goes out with about 5 dogs every day plus any that he meets so he has regular contact plus regular socialisation classes so not sure why he hasn't learnt some doggy ettiquette.

The problem is that because he runs so fast it takes him a while to stop himself and because he doesn't apply the breaks in time he will either end up running past the dog or actually crashing into them! If the dog stands his ground then he actually ends up ignoring them when he gets there, which makes me wonder why he went in the first place, but if the dog runs as he approaches then he'll chase them for a bit. He is quite dominant over dogs and doesn't read them particularly well. I also worry that a dog won't appreciate his rudeness and will bite him.
I do leash him when I come across unfamiliar dogs which is all the time but it means that I rarely let him interact with them which makes him leash frustrated.
He also doesn't know how to play with dogs, if he can chase them then he's happy but if they chase him he doesn't like it and tries to come back to me and doesn't know what to do. I much prefer it when it's that way round though.

Mmmm - you can actually teach dogs to change gait. For instance to change pace for obedience competition I teach my dogs "walk" for slow pace whereas normal and fast pace they prance (for lack of a better expression).

I know handlers that have also taught their dogs to canter for HTM routines but whether you could actually teach a dog to do it in the situation you describe would be challenging....!!

When approaching dogs, I keep my dog on a lead and as soon as he pulls I stop still, he sits automatically then I carry on. He doesn't get up to walk until I pass him, he'll pull again to greet, I stop, he sits and we carry on.

When he starts to walk a bit more calmer towards the dog I say "slowly" and repeat this whilst praising, his ultimate reward is to say hello to the dog. If however it gets too much I will turn him away to regain his focus.

This is getting better by each day, if he's on the lead and I say "slowly" he will walk 70% of the way towards the dog without pulling.

Once I've achieved this on the lead, it'll be time for me to teach him off the lead.

Though he has 100% recall so I always call him back when he goes running full belt toward a dog, lead goes on, and we practice greeting calmly on a lead.

Do you own my Halle?

For leash frustration long line is brilliant, it isn't for recall it is to remove tension and gives a dog more freedom. No ruining on long line, lurchers are too fast and too fragile.

NicoleW that kind of approaching other dogs isn't good for lurchers, they get frustrated and that how aggression starts. My Halle with every single second
when she is on lead and sees other dog get only more and more annoyed, so when finally she meets a dog, she is snappy. This road is leading to leash reactivity and leash aggression.

alexpb22 maybe emergency stop will helps? You will shout stop before your dog crushes into another dog.
How to teach it:
put a dog in sit position, ask him to wait and move away from him. Have a treat (big cube) in your hand, call the dog to you. In half way in the same time:shout stop, rise your hand, this with treat and stretch it out and thrown treat. You should finished with stretched out hand and palms straight. Dog will stop to find a treat. Don't worry if he can't get it at first place, but he is a lurcher so he will see flaying treat
If dog starts slowing down when runs to you, do only recall few times and again try to do emergency stop. When a dog gets idea of this command, you can stop to thrown treats, he can have it when he comes to you.