He received an undergraduate Master of Arts from the University of St Andrews before serving for two years as full-time Scottish Regional Secretary of the Student Christian Movement.

[5][6] In 1983, Gardiner was awarded a Kennedy Memorial Trust scholarship to study philosophy at Harvard University[2] under John Rawls, returning to conduct doctoral research at Corpus Christi College, Cambridge for three years from 1984.

[2] Gardiner contested the Greater London constituency of Brent North at the 1997 general election, defeating the incumbent Conservative MP Rhodes Boyson by 4,019 votes.

In 2004, he was appointed Parliamentary Under-Secretary of State at the Northern Ireland Office, moving to the same position at the Department of Trade and Industry following the 2005 general election.

He moved to the Department for Environment, Food and Rural Affairs in a May 2006 reshuffle and left the Government in June 2007, to once again serve as a PPS, this time to the Business Secretary.

[2] He left this role "by mutual consent" on 13 September 2008 after joining other Labour MPs in declaring an MP should stand against Brown, accusing him of "vacillation, loss of international credibility and timorous political manoeuvres that the public cannot understand".

[10] After the 2010 general election, the Independent Parliamentary Standards Authority published new expenses rules replacing funding for a second home with a London Allowance of £3,760 for MPs with seats within 20 miles of Westminster.

[17] In June 2013, Gardiner and Conservative MP Tim Yeo jointly tabled an amendment to the Energy Bill which proposed establishing by 2014 a decarbonisation target for the UK's electricity generating sector, to be achieved by 2030.

[17] In this role, Gardiner criticised the lack of prosecutions of leading players ten months after David Cameron promised that everything possible would be done to deal with crime relating to the horse meat scandal.

"The extraordinary thing is that because of its clout, industry has been able to commit what appears to be a criminal offence – selling the public horsemeat falsely labelled as beef – and just say they are sorry and didn't know".

[20] In January 2015, he admitted the push by the previous Labour government to encourage car-buyers to opt for diesel vehicles in a bid to protect the environment was "wrong", identifying that a "massive problem for public health" had been created.

[21] When Jeremy Corbyn was elected Leader of the Labour Party in September 2015, Gardiner moved to becoming Shadow Minister for the Department of Energy and Climate Change.

He urged Theresa May to tell China that Britain wanted strong investment in infrastructure projects and described her decision to halt the deal as "politically stupid" and tantamount to "closing UK Plc down".

[26] The US Department had suggested the solution was a 300% tariff on Bombardier CSeries being sold to Delta Air Lines, which would adversely affect prospects for the sale.

[30] Boeing replied their illegal-subsidies complaint against Bombardier was about selling aircraft below the cost of production and not anti-competitive, saying it merely wanted "fairness" in "following trade rules".

[39] In 2017 The Times revealed, from September 2015 to February 2017, Gardiner had received £182,284 in disclosed cash donations from Christine Lee & Co, a firm of solicitors which acts as the chief legal adviser to the Chinese embassy.

The paper also revealed part of this money was used to fund the employment of Daniel Wilkes, son of the firm's founder Christine Lee, in his parliamentary offices.