Hi, sorry I was offline by the time you replied last night. The main issue in your situation is that it was specifically agreed that this was going to be a temporary change an even though it was initially agreed it would only last for 6 months, the fact it has continued for a further 9 would not necessarily give you permanent rights to it.
There is a principle in law known as custom and practice where if something has been consistently applied for a prolonged period of time and it is clear that these were the intentions of both parties, it could become an implied contractual term. However, I am not convinced you have the requisite factors to argue that – 15 months is not a long time in legal terms, the employer never formally indicated that they had intended for you to be in that role permanently and the delays were due to other reasons which meant the person who originally did it could not return on time and in general there was no indication that this was ever going to be permanent. So this argument, whilst something you can raise with the employer, is not going to be that strong.
In terms of being paid more for the work you did, again this is not going to be easy. It was never agreed that you were going to receive any higher pay whilst working in that job. You never challenged the fact you were not being paid more and it would lead to an implied acceptance on your part that you were happy with what you were getting paid throughout this time.
Finally, in terms of constructive dismissal, you must demonstrate a fundamental breach of contract on the employer’s part, but if you cannot easily show that you had gained permanent contractual rights to that position, then such a claim could be quite risky. It does not mean you cannot resign and try pursuing it, but I certainly cannot say that you have a strong enough case to say you should definitely consider it.
Hope this clarifies your position? If you could please let me know that would be great, thank you
you are welcome