OOOO this thread will run & run
I'm making no comment but will watch with interest

Made (mad passes the spell check)

I would say NO

Just to add another one, had a guy sneeze once - pulled something in his side he thought, less that 15 mins later he was on his way to hospital with a collapsed lung.

Was totally uncertain about reporting or not, so called the unhelp line who suggest it was a workplace injury and therefore needed to be reported.

Oh the fun we had with the Local EHO........

In your case, and with my experience I would fully investigate, use Occ health if you have it to determine any medical history and keep the investigation on file, however this is a no from me too.

Did I ever tell you about the time I had a guy run away from a wasp straight into a door and dislocate a shoulder.....oh how we still laugh about that one....

Hi Tigers, I would have to go with the majority of other posts on this one, had one similar recently and did not report, also pre existing conditions are given better coverage in the latest regs.
Good luck.

How was this not work related, it happened in work. It could have happened when he/she got off the chair at an odd angle. There is no way this can be a flat NO. It is nonsense, as employers they are responsible to investigate Accidents. I dont mean to preach Legislation but it seams people are not thinking here. I say discuss it with the HSE.

I would say email or call the RIDDOR deptartment and explain the situation. I have dealt with them on a number of occasions, they are very helpful.

Ryan, I appreciate that but your response was a bit scatter gun to say the least hence my points.

I'm fully aware of what duties RIDDOR places on employers and in this example the, IMO, would not be notifiable.

We can only go on the information posted by the OP do you honestly think that this matter is going anywhere near a criminal court for failing to report? That's what you suggested in you response and example! Further suggesting that failing to notify would support a civil matter.

Back to the HSE. Who is the OP going to talk to? The telephone service a Caerphilly ceased a while back, I revert to employers duties at this point! Note the OPs details 'public services' chances are they are regulated by the LA.

If you involve any regulator in the decision making process around notifiable matters they will in the most cases advise report, hence my comment about employers duties.

The accident must be work related... It's in the interpretation of this statement that you will find your answer.
The key aspects that will help you decide this, are questions like:
The condition of the site or premisses where the accident happened?
The machinery, plant, substances or equipment used?
Any historic information, is it an old injury caused through work that she has agitated?
If all of these point to it being a freak accident totally unrelated to her surroundings then I wouldn't report this.
You will still be required to make a report and keep a record of this, if you complete an accident book then this will suffice.

It's not actually cited anywhere that I am aware of, but would it not be prudent to consider it all the same? Much in the same way you might dismiss a personal injury that becomes an issue within work.
If she had broken her ankle whilst tripping over some loose carpet 6 months previous and it was the old injury that had flared up again, this would be regarded as work related. If it simply just gave way, and none of my previous comments were involved then I wouldn't report it.