Not sure if this is the right place, but....

[IWantWine]

If an employment contract stated that hours of employment were only one hour per week (yeah I know!), but, actual hours of employment were over 20 per week for say, 18 months, would this set some kind of precedent and have any influence over the 'contract'?

I am concerned about my situation at work.

We are due a 'bonus' but it is only paid to us under certain circumstances, which I feel are vague and favour our employer.

Not enough, if any, of us are in a union, other employees have found the union totally unsupportive in the past so I dont see that as an option.

Feel free to ask for more info, I am just reluctant to give out too much, except to say that my career choice has been featured in the news lately.

Family members once worked for a large retail group where they were only contracted for 4 hours a week, but the expectation was for very many more than that. The contract stood, any implication that the hours worked formed any implied terms were not accepted.
If my experience is anything to go by you are possibly deemed to be working more hours just because you want to.
Sorry if that's not a lot of help.