Apparently Nick Clegg approached Martin Bell and also the editor of the Eastern Daily Press both of whom turned him down.
I was going post my thoughts on this but Nich Starling has said pretty much what I was going to.
I will just add that I seem to recall 18 months ago that there were lots of people approached about the Conservative London Mayor candidate position before they finally accepted Boris as the candidate. It is by no means unusual during a high profile election (like any by-election) for parties to try and raise their profile by going for a well known national or local figure.
I am sure the Tories will try and use this against April Pond but I am really not sure there is much mileage in this story.