Mandelson's charm offensive: a disguised dagger in Brown's back?

Will Brown follow Mandelson's lead and try to take the heat off Clegg tonight?

Mandelson's line at lunchtime was basically: Nick Clegg is as infallible as the Pope, or perhaps a little more so.  Anything else is just Tory smears.

Why is Mandelson quite so keen to shield Clegg?

Theory 1 says that Mandelson wants to puff up the Libdem vote simply so Labour can do its arithmetic trick: 3rd place in the share of the vote, first place in terms of seats. Labour stay in power, propped up by 100 Lib Dem MPs.

Theory 2, though, says that Mandelson reckons Clegg will never agree to support a Brown-led Labour minority government. But by buttering up Clegg now, Mandelson is preparing the ground for his own post-election coup:

Here's how it works:

• The election produces a hung parliament, with Labour the largest party in terms of seats.
• Clegg says no to a deal with Brown.
• Brown resigns as PM.
• Clegg lets it be known that a deal with a Mandelson-led Labour government would be acceptable.

Couple of problems:

• Mandelson doesn't have a seat in the Commons. He'd find a way around that. An immediate second election would find him a seat, and the Lib-Lab coalition would romp home.
• Labour MPs wouldn't like a Mandelson + Clegg stitch-up very much. But if that was the price for keeping the Tories out of power, perhaps forever - well, I think they could just about live with that, don't you?

Brown surely knows what Mandelson is up to. So how's he going to play Clegg tonight? 

Let's watch.