I am thinking about writing a program to check some mileage claims (about 45,000 of them actually) made by Members of the British Parliament recently.
The data I have is quite course - the origin and destination of the trips is generally provided only at the Town level. What I am looking to do is basically look at the mileage figures they have submitted, look at the "calculated" mileage obtained from a web service, and then compare / contrast. (I'm thinking of perhaps being interested in cases where the claimed mileage exceeds 40 miles, and the claimed mileage exceeds the website figure by a factor of at least 1.4 for instance).
Code wise I'm fine, but what I don't have is a webservice I can use to get the distances. Google Directions is out of the question (has to be used with Google Maps) - and I am looking at writing this as a console app in C#.
Can anyone suggest any suitable service?
You should take a look at any routing services that are using Open Street Maps. Many services based off of OSM are provided free of charge and are less restrictive than Google Maps.
One that I can think of is Open Route Service, though I don't know if they have a permissive API that allows you to do what you're asking.
If you are working for a government entity, many of them have licenses for Esri ArcGIS which includes a street data, turn-by-turn routing directions, and an API.