CM,
While not defending MPs, I would point out that their job requires them to work at two places at once - yours did not.
If the RAF wanted you to work at Leuchars, you worked at Leuchars. If you elected to keep your family at Lincoln while you did so that was your choice, but you had to pay for it.
By contrast, an MP is elected to represent his constituents. An MP for Fife is required to work at Westminster, but also to be available in his constituency in Fife to meet his constituents. He is required to work in two places at once, quite far apart. The system of housing allowances was attempting to cater for this - note that MPs within a certain commutable distance of central London got no such support.
Having said that, they all beneath contempt in my opinion, and are largely self serving individuals I would quite happily see thrown on the scrap heap!