TIMELINE: The highs and lows of British PM Brown

(Reuters) - British Prime Minister Gordon Brown faced a new threat to his leadership on Wednesday after two former ministers called for a secret ballot of MPs to decide if he should step down before an election due by June.

Here is a timeline of Brown's ups and downs since he took over from Tony Blair on June 27, 2007.

June 30, 2007 - Brown is praised for his calm and steadying response when Britain goes on its highest level of terrorist threat warning after two car bombs are found in London and two men crash a jeep into Glasgow airport.

Aug 12 - A poll gives Labour its biggest lead over the opposition Conservative Party since before the 2003 invasion of Iraq. Brown also wins plaudits for his urgent response to the worst floods in 60 years and for his swift action over an outbreak of foot and mouth disease in cattle.

Oct 6 - After mounting speculation, Brown rules out an early election as opinion polls show the Conservatives erasing Labour's one-time 11-point lead. Analysts see the "bottled election" as the beginning of his descent in popularity.

May 1, 2008 - Labour slumps to its worst local election defeat in 40 years. In London, Labour Mayor Ken Livingstone is beaten by Conservative Boris Johnson.

Oct 3 - Brown revamps his cabinet, winning praise for boldness by recalling former political opponent Peter Mandelson as Business Secretary.

Nov 6 - Labour wins a surprise by-election victory in the Scottish constituency of Glenrothes, which some see as a sign Brown's handling of the financial crisis has revived his political fortunes.

Feb 24, 2009 - Brown's government faces a major revolt among his supporters and a union threat of a strike over plans to sell a stake in state-owned postal services operator Royal Mail. In parliament, 145 MPs, mostly Labour, sign a motion opposing the part-privatization of Royal Mail.

March 29 - The government takes a knock as Home Secretary (interior minister) Jacqui Smith, already under investigation over her housing allowance, apologizes for using public money to pay for adult films watched by her husband.

April 2 - Brown basks in the international spotlight as he hosts a G20 summit in London which agreed to pump an additional $1.1 trillion into the troubled global economy.

May 14 - Elliot Morley, a former Labour government minister, is suspended in the latest of a series of embarrassing revelations over parliamentary expenses. News overshadows Brown's launch of Labour European and local election campaign.

June 2 - Home Secretary Smith resigns. The next day Communities Secretary Hazel Blears resigns. Six senior ministers eventually resign.

June 4 - European elections give Labour its smallest share of a national vote in 100 years

June 5 - Brown reshuffles the cabinet to secure the loyalty of several ministers and averting a government collapse following the expenses scandal.

June 8 - Brown beats off a challenge to his authority, winning over Labour members of parliament after admitting mistakes. "I know I need to improve," Brown tells 350 MPs.

August 29 - Brown visits troops in Afghanistan to counter criticism that the war effort is being undermined by a lack of equipment and personnel.

September 15 - Brown concedes he will have to cut spending in order to tackle Britain's soaring debt, but promises voters "vital frontline" services will not be affected.

September 27 - In a television interview Brown denies political gossip he is taking prescription painkillers or pills and says he is fit enough to lead the country.

September 29 - Brown tells supporters at the ruling Labour Party's annual conference they have a duty to stand and fight and win.

September 30 - The day after Brown's conference speech, Britain's top-selling daily newspaper The Sun, part of Rupert Murdoch's News Corporation media empire, announces it has switched its support to the Conservatives, saying "Labour's lost it."

January 1, 2010 - The opposition Conservatives hold a double-digit lead over Brown's Labour according to the first poll in a year Britain must hold a parliamentary election. The YouGov poll puts the Conservatives on 40 percent and Labour on 30 percent, which would give the opposition a small majority.

(Reporting by Michael Holden)