The Liberal Democrats, who launched their manifesto this morning, are having an undeniably good week.

First, they are gaining in the polls, with -- among other things -- more people apparently wanting Vince Cable to be Chancellor than George Osborne, and a sizeable number seeking a hung parliament.

Secondly, and no doubt thanks to a very large extent to Cable, they have produced what should be hailed as a credible economic programme. My excellent colleague Sophie Elmhurst is right to highlight the rather absurd regularity with which Cable talked of "elephants", describing the deficit as the "elephant in the room" and appointing himself the "elephant man" to tackle it. But there is one serious point here: the Lib Dems say with some justification that they are the only party to have fully costed their plans without any reference to "efficiency savings". This is likely to enhance their growing popularity.

Nick Clegg, who held his own against Jeremy Paxman this week, has undoubtedly matured as leader, just in time for an election in which his party is looking a formidable force again.

Some in the party feared that after ousting Charles Kennedy, with his distinct opposition to the 2003 Iraq invasion and his bold pledge for a penny on income tax, the Lib Dems had lost their direction. But now, with Clegg's own openness on tax aimed at taking 3.4 of the poorest out of paying it altogether, his shadow chancellor who reaches to otherwise alienated voters and his clear message of "fairness", this interesting party is very much back in the game.