Understand what you are saying Jambutty, one of your queries was conflict of interests though.
In the case of Mark Lancaster, he is only 38 years old, and probably more than capable of handling other activities. (Not that is always an age thing mind you, lots of over 50's capable of producing lots of energy).
Like I said earlier, would be interesting to see how many M.P's do engage in another career quite heavily. Don't suppose any sort of list like this is available though, without going into each one individually .. unless MargaretR can google us one ...
At the end of the day, presume doesn't really matter if they do their duty to the electorate, who would no doubt pick up if their local M.P. was not pulling his/her weight. Suppose would have to be something like not being able to attend an important Common's meeting, etc., due to prior business commitments.