I suspect Brown was thinking, as a fan of US politics, that it might be nice to have a powerless opposition figure or two in his cabinet
He was perhaps just looking across the Channel, where Sarkozy is using this tactic to smoke-screen the place up and look like he's more consensual than he is... When locusts move on, they leave nothing behind
But in a bipolar political system, which is nearly inevitable in a unitary circumscription, first past the post electoral system -- and Britain invented both the system and the result -- a centrist party has little to no chance of winning power. 55% of the country wanted Bayrou to be president, but only 18% of the country was willing to vote for him personally and only 5% was willing to vote for his candidates.
The model for the Liberals ought to be their long ago predecessors who held power for at least a generation after they no longer had anywhere near a majority of the electorate (due in part to their own efforts to push through the 2nd and 3rd Reform Bills). They overcome the consistent support of petty merchants and agricultural workers for the Tories by forming the Union with the then-nascent Labour party. (In France, the same was true of the radicals and socialists in the same period.)
So whatever this means for Brown, it certainly means that the Liberals will remain a distant third in all except a few localities.
