Cleaning up Politics

If memory serves me correctly, during the General Election last May David Cameron campaigned to cleanup politics.  He was largely but not exclusively referring to the MPs expenses scandal.  I wonder therefore how it is that in the Finance Bill published on 29th March 2011 there is a specific clause that excludes Members of Parliament from legislation regarding tax avoidance by means of disguised remuneration.  Hidden deep in the small pring of this 390 page Bill is sub clause 554E (8) which reads:

"Chapter 2 does not apply by reason of a relevant step taken by the Independent Parliamentary Standards Authority in relation to a member of the House of Commons."

There has been some comment on the inclusion of this strange clause in the Finance Bill, mainly from fringe internet blogs; the only comment I have found in the mass media is this item from Ian Cowie of the Daily Telegraph.  To the best of my knowledge neither the BBC, ITV or Sky have reported on this matter.  In my opinion this indicates that the health of our democracy leaves much to be desired.  However even if there are only a few of us asking the question it still needs to be asked.

Why do MPs need to be exempt from a law designed to prevent tax avoidance?
Best Wishes
Will