But a relationship with the United States based on the flawed principle, "my ally right or wrong" is not only profoundly illiberal but will be unsustainable as well.

[10] Campbell's early performances at the weekly Prime Minister's Questions were criticised,[11] leading him to declare himself "perfectly confident" that he could fulfil the role of party leader.

[12] Campbell regained some ground with the controversy over the US practice of "extraordinary rendition",[13] the case of the NatWest Three,[14] and the conflict in Lebanon.

[17] The University of St Andrews awarded an honorary doctorate of law to former President Mohammad Khatami of Iran, which sparked some criticism, although as Chancellor he is only the titular head and not involved in such decisions.

Brown surprised Campbell by requesting that two Liberal Democrats (Lord Ashdown and Lady Neuberger) join his cabinet.

After taking 24 hours to consult and consider, Campbell rejected the offer as unworkable, given the gulf between the parties on issues of foreign policy and civil liberties.

Labour leaked news of the meeting to the media and went behind Campbell to offer the job of Secretary of State for Northern Ireland to Ashdown anyway; he turned it down.

Following this announcement, Campbell's leadership again came under question, with some in the party feeling that now the heat was off the time was ripe to get a younger leader potentially more capable of connecting with voters.

Alongside him was deputy Leader Vince Cable; they praised Campbell's leadership and said the party owed him a debt of gratitude.

In his letter of resignation, addressed to Hughes, Campbell stated, "It has become clear that following the Prime Minister's decision not to hold an election, questions about leadership are getting in the way of further progress by the party".

[30] Liberal Democrat Leader Nick Clegg paid tribute, saying Campbell "served this country and our party with unparalleled distinction".

[31] There was speculation in 2013 that he would be offered a seat in the House of Lords[31] – an opportunity in which, during an interview with Chat Politics, Campbell declared his interest.

[34] He has been critical of what he claims as the "disproportionate military action" employed by the Israeli Defence Force in Gaza and in Lebanon, contending that Israel's tactics exacerbate existing tensions and lead to human rights abuses.

[15] Though a supporter of Anglo-American cooperation, Campbell has argued that the Bush-Blair relationship was one-sided and that the Labour government pursued it at the expense of Britain's standing in other international institutions, particularly the EU and UN.

Campbell had stressed the need for the Liberal Democrats to provide extra support for female, disabled and ethnic minority candidates seeking to contest winnable seats.

Campbell is a member of the Top Level Group of UK Parliamentarians for Multilateral Nuclear Disarmament and Non-proliferation, established in October 2009.