Welcome to the communities.

It’s really hard to give any real practical advise as the details given in your post are so limited.

Broadly speaking there are two sometimes conflicting things here

One as a professional you have a duty to comply with both the law and our professional code. If you are asked to do things which are clearly in contravention of these then you need to raise the issues and object. But it’s often a fine line and can be a judgement as to if something is unwise or risky rather than actually unlawful. If you are asked to do something actually illegal you of course should not comply.

The second issue is what happens when a manager doesn’t follow your advise - and that is quite different. Managers dont follow HR advise all the time. It’s not then open to HR professions ( subject to the point above) to take their bat and ball home and not play anymore. Your obligation is to continue to do the best you can for your firm within the law. That may well ( and often does) involve digging managers out of holes they created. It sometimes does involve doing things we would prefer not to ( but staying within our code and profession).

On this one I would probably insist that the manager and I JOINTLY saw the employee to extend their probation ( and of course probation has no real legal basis) and I would try and coach the manager into dealing with their mess and cleaning up after themselves but with my help.

In reply to Keith:

Hi Keith thanks for the reply. I have raised my actions that the behaviours are unlawful and against my code of conduct however they wanted to continue down the line regardless of the risk. Due to their delay in the process the employee has now raised concerns they are being discriminated against and they are now trying to backtrack. I will assist in the meeting but feel the Manager should be leading this as my complaint is HR gets a bad name as I always end up the person having to lead meetings as the managers are not trained/nor want to hold difficult conversations. Much appreciated

In reply to MRS JACKIE DONALD:

Good luck

Sounds like number one on list of things to do for 2019 is sone solid management training.

For what it’s worth most employees see through HR giving the messages to the real organiser.

Welcome to the community Jackie.

Ace advice from Keith as usual. "I did say this would/could lead to problems....." would be something I couldn't possibly leave out of the conversation you will have with the manager/s.
And I insist on having the manager with you - He's the one who is extending their probation.