As per Steve's answer, the mileage you have actually done is negligible.
I've seen people that have stated that they do 1000 miles per annum, but when their documents come in, it's been closer to 20000!!!
We usually allow for up to about 2000 miles over the disclosed amount, as you never know if someone has a personal situation that means that they will go over their declared milegae (ie frequent hospital trips), but anyone found extracting the urine only gets a slightly increased premium to cover the increased risk - it's highly unlikely that it will actually affect your cover.
When working at my previous employers, we used to deal with classic policies - these were very strict policies, and limited mileage polices were really scrutinised. However, as previously stated, going over your declared mileage isn't that big a deal in the grand scheme of things.