Whilst unlikely, insurance companies can and will check on mileages if they suspect fraud or can wriggle out of paying a claim. They can ask to see MOT certificates which carry mileage data and also service records to check that the car is maintained and fit to drive on the road - these also carry mileage data. The reason that they ask for mileage per annum data is that obviously the risk of accident is statistically related to the mileage driven and so a deliberate under estimating of your annual mileage on your insurance proposal could be looked at as an attempt to provide misleading information and to nullify your policy. The insurance companies aren't going to be interested in excuses about 'girlfriends oop north'. In dealing with insurance companies it is better to play it safe IMHO.