Many thanks for your patience. In the circumstances there is unfortunately no straightforward answer as there are no specific laws dealing with this situation. It is a mixture of different factors and practices but the process of slotting people into other jobs is really an internal matter governed by internal policies. The law only looks at what is generally fair and reasonable rather than the exact specifics.
I think in the circumstances the best argument would be that of custom and practice to say that you have worked in the job for long enough that it has become your implied position. Not always an easy argument but nevertheless one that you are free to raise.
This principle makes implied terms them contractually binding even if they are not written down anywhere. This area of law is rather complex and it is usually only down to the courts to establish with certainty if something had become an implied term. Nevertheless, it does not prevent employees from directly raising this argument with their employers.
The basic requirement for implying terms is the presumed intention of the parties, in other words - did the employer and employee intend for the terms in question to be treated as contractual. In general, a practice would need to have been clearly communicated and consistently applied for a substantial period of time before it can be considered an implied contractual term. Therefore, something that is uncertain, not communicated properly, not been applied consistently or has just been around for a few months is unlikely to qualify.
This is your basic legal position. I have more detailed advice for you in terms of what case law has determined as important factors to support such an argument, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you