Let's be clear though: what you have suggested is not even opinion, but the foisting of a scenario from a different case onto this one.

I think we could deduce that her boss was a clown by the fact the words works for local authority were used

Just looked up my companys for an example

... is very much. You're assuming, for instance, that the boss did not decide to make the call off his own bat.

You don't know that. Neither do I. He might have been told to do it. He might not have. But you're making an assumption.

Any of that SHOULD be done when someone returns to work or be dealt with by HR, the manager here has over stepped his authority.

Lets have a think about this

I know where you work, you know what I do, we both know what ROBINSON does.......

waste of time anyone?

I'd say lettings are a bit quiet and the girls in the office are having none of his "shenanigans" after the whole Rennard thing...

Hope you get things sorted.

Whats Malcolm Walker go to do with this ?

I've done more than my fair share of disciplinaries over the years and effectively handed out a few P45s as well within private industry (they all deserved it btw...).
However I'm struggling to think of how the proceeding events ended up with the line manager of an employee (who has a broken leg from a work place incident that also might well be her employer's fault) rings up to tell said employee that she is getting a formal warning for what is clearly an unreturnable injury.

Even with the flag for number of days absent there is no plausible scenario (that I can think of) that would even remotely allow this to happen given the facts (on the face of what Rover49 has stated)
Firstly don't worry, she has done nothing wrong and is not in any trouble whatsoever, it clearly looks like mismangement and the line manager is a plank for not questioning such if he has had an instruction to ring with a formal warning.
If you can remember take a note of the time of the call and write down who said what to the recipient at your end.
Wait to see what if anything comes through the post, in the meantime contact your union representive and have an informal chat about the events as they happened and let them do the work to find out why someone is ringing you up threatening your wife with a formal written warning.
Hopefully will hit the fan and profuse apologies to follow (choccies and flowers wouldn't go amiss)
If you get no joy from the union (unlikely) contact ACAS and/or Unison direct at head office, I think that is the union involved for the local authorities..
good luck and get well for t'other half..

any news rover49?

Good stuff.