It's none of the above - the contract has always stated an hourly rate for standard 39 hours, and the same rate for over that.
In a new agreement, an annual figure has been agreed, but when I extrapolate the 39x52xrate shown on payslip, I come up with slightly less than the agreed amount.
There seems to be a complex calculation in place that nobody internally fully understands. I think it's [((salary/365)x7 )x52]/(39x52). Actually, doing that just now has given me the same value as the lesser rate x 39x52.
It's not a significant amount, but would cover a bill each year, and it's more the principal of the matter given the sacrifices I have made for the company, particularly over the past 4 years.
I suppose my question is how common is this, that your agreed salary is not what you actually receive gross, based on an abstract calculation that I didn't think existed outside the public sector (I remember in a public sector job, people would finish on random days like Mondays, as pay was calculated over 7 days).