Andrew Grice: Uphill battle awaits Ming the lonely

When Sir Menzies Campbell stood up to speak in the Budget debate at 1.43pm yesterday, there was a sudden exodus of MPs from the Commons chamber and the public and press galleries above it.

Being leader of the third party is never easy in a political system devised by, and for, the big two parties. It is even harder on set-piece occasions. At Prime Minister's Questions every Wednesday, David Cameron always gets called before Sir Menzies, so the Liberal Democrat leader knows Mr Cameron will probably go on his number one issue and must often raise his second choice.

Yesterday, the judgement of his own MPs was that Sir Menzies answered the sceptics who wondered whether he could translate his expertise in foreign affairs to the domestic arena as he focused on the council tax, pensions and the environment. He said more about the Budget measures than Mr Cameron.

However, that exodus from the chamber highlighted a problem facing Sir Menzies. Even though all three parties will have new leaders at the next election, there is a danger that the media and therefore the public will be fixated by the battle between Messrs Brown and Cameron.

Even friends believe privately that Sir Menzies' biggest handicap may prove his age, especially if Mr Cameron can convince voters that his relative youth is not a disadvantage. When he speaks about pensions, the Liberal Democrat leader, who will be 65 in May, is cruelly ribbed by Labour MPs. However, he may yet have the last laugh if he can garner the grey vote; there are 11 million pensioners in Britain. As he is quick to point out, more than half the population will be over 50 at the next election.

His next big test will be at the 4 May local elections in England, mainly in urban areas. This will provide a useful dry run for the general election, when the Liberal Democrats' best hopes for gains will be from Labour in its traditional heartlands.

Allies hope Sir Menzies will be well placed to prevent the Tories regaining former seats now held by the Liberal Democrats. So he will have to appeal to both Labour and Tory-leaning voters at the same time, a tricky task, while trying to fend off difficult media questions about which way the third party would jump in the event of a hung parliament.

* Treasury Budget site

* Chancellor's Statement in full