I've recently run into a dispute for an invoice with a company for whom I'm doing IT contract work about the number of hours in a work day. We agreed on a rate of £N a day, which I had assumed to mean N/7.5 as an hourly rate. However, they have recently said that "everyone contracting here assumes an 8-hour day". The contract that I signed doesn't state either way which one is correct. However, if I adjust said invoice to assume an 8 hour day, I will lose 6.25% of my revenue (assuming my maths is correct).
Without this being specified in the contract (or verbally at any point before today), is it legally acceptable to state that 7.5 hours is the standard amount and that I should bill as such, and what can I do about resolving this issue?
Also what should be done about going into the future with this work and asking for a revised contract? Can I request 6.25% to be added on to my day rate, or ask to be billed on a 7.5 hour basis, and have that stand up against their legal team if push came to shove?
I am invoicing on an hourly basis rather than by half-day/day, and have done many hours of overtime.
Thanks in advance for any help.