Is Milburn planning a leadership challenge?

According to Mike Smithson at Political Betting, Alan Milburn may be planning to challenge Brown for the Labour leadership, in the aftermath of the Crewe and Nantwich by-election. Says Smithson:

“I cannot vouch for the accuracy of this but it comes from somebody I trust who has very close links within the party. Clearly something is going on out there and this weekend would be the ideal time to strike.”