Does a temporary arrangement become permanent if both parties just continue with it?

[JonasJones]

Hi, I worked full-time for an employer for 15 years before deciding that I would like to go part-time. My employer agreed to trial the part-time arrangement on the basis that it would be formally reviewed after 6 months, before deciding if it could become permanent. This is all in writing and a new part-time contract was signed. However, my employer did not conduct a formal review after 6 months and I continued to work part-time for an additional 3 months for a total of 9 months since the arrangement began. My employer is now saying he wants to end the trial and take me back full-time, which took me by surprise because as far as I was concerned the trial period had ended 3 months ago and that for 3 months I had treated the change as permanent. I want to ask if my employers failure to conduct the review after 6 months (and by me continuing to work and be paid a part-time salary for those additional 3 months) constitutes his acceptance of the change and that I could expect it to be treated as permanent. Thank you.

[ULA]

No not necessarily. It was clear given the arrangement that this was to be reviewed after a six month period albeit this did not happen. By both of you continuing the arrangement without formal correspondence this does not make it permanent. Arguably you could have spoken to your employer at 6 months to confirm that the situation.

If this working arrangement had gone on for a longer period then there may be an argument that custom and practice would have "kicked in" however not so sure this would be the case after 3 months, particularly given the circumstances over the last 3 months.*

[JonasJones]

Thank you. Can I ask one last thing, in this situation would the employer have to give any notice to suddenly end the extended trial period or could he do it immediately?

[ULA]

I would suggest that your employer should give you notice of the change to the current situation given that they did not review the position at the six month mark.*