Every party has one and they're usually too difficult to spot.
I think Labour used to have Mike O'Brien who seemed to be the only person constantly wheeled out, as apparently the only person 'available' (or actually willing) to defend the singularly disastrous party line on Iraq.
The Tories used to seem to rely on Justine Greening, who again always seemed to be the person put up for interview or comment, seemingly, as and when required.
Apparently ever willing to paint the picture of success on the canvas of failure, of anything and everything, with vigour.
I think Anna Soubry has filled her shoes recently though.
Every time I see her on the T.V. she has nothing but good to say about, well everything really it seems.
Or more to the point, all things Conservative.
There are only a couple of prerequisites for this unofficial position.
They must have an unlimited capacity for the ability to endlessly waffle, whilst also retaining the ability to relentlessly extoll the pseudo virtue of every facet of any given subject, in the face of adversity.
This they must do, with gusto and enthusiasm.
It also helps if they are the type that will blow in the policy wind with few, or better still no strong, ideological principles of their own.
These will be best enabled to regurgitate the party line and espouse success where there is failure, with ease and a clear conscience.
Obviously by definition, the only other profiling requirement is they must have a desire to further their own career.
Thus, they can subsequently be relied upon to don the blinkers and blindly defend the indefensible, come what may.