It has been an honour and a great privilege to lead the party over the last three years and to be part of the first generation of Liberal Democrats to be in government in Britain since the Second World War.

BBC: Nicol Stephen resignation in full

That will also make the televised debates of the three main party leaders a first in a British general election a crucial part of the campaign.

ECONOMIST: Why the campaign will count in a contest that matters

Analysts say the results of the first opinion polls since David Cameron's Conservative Party speech are likely to be a crucial part of the PM's calculation.

BBC: NEWS | UK | UK Politics | Cameron seeking Whitehall talks