Just wanted to close the loop on this thread.
Pool was emptied and broken tiles replaced. I took the opportunity to hunt around for the source of algae, and found a fair amount behind the solar provision covers which I have now left off, and a small amount inside the drain which wasn't properly cleaned the first time.
I gave the pool a good scrub prior to filling, and it's now been algae free for a couple of months. Having said that we're just coming out of winter, so it's had no use and FC had been at 14ppm with the chlorinator at the lowest setting.
Thanks for all the help.