Image copyright Getty Images Image caption Lord Owen was foreign secretary from 1977-1979

Vote Leave's Lord Owen has dismissed the "voices of doom" warning against Brexit and said the sooner the UK can quit the EU, the better.

He said the quicker it began, the less likely the UK was to be "dragged down" should the Eurozone collapse.

The former SDP leader accused Downing Street of "manipulating the FTSE 500" to back the Remain campaign.

The Bank of England, the IMF and Barack Obama are among those to have warned about the impact of a British exit.

A Treasury analysis suggested the UK economy would be 6% smaller if it left the EU than it would otherwise be by 2030, which Chancellor George Osborne said would leave a £36bn hole in the public finances.

'Ridiculous'

But in a speech in London, the former Labour foreign secretary and SDP leader Lord Owen said: "There is no fine calculus that can weigh up the consequences of either [remaining in the EU or leaving].

"Economics is not pure science, there are too many behavioural consequences to assess. Almost all the forecasts are ridiculously short-term."

The peer, who backed Britain's membership in the 1975 referendum, dismissed Treasury projections as "ridiculous".

He accused No 10 of "manipulating the FTSE 500 corporates" during EU negotiations - referring to a letter from the boss of Serco to David Cameron mentioning how EU support could be "mobilised" among some of the UK's largest firms.

Lord Owen said: "With few exceptions, the voices of doom we hear today were telling the British people 17 years ago we had to join the euro."

He added: "Technically anyone can always predict a short-term hit to the economy if one pre-supposes a big enough psychological or confidence set-back."

But he said in the long term, other factors were more which influenced the economy such as "the pace of technical change and other influences on 'total factor productivity'".

He suggested Britain could save £10bn a year - about £190m a week - by leaving.

Vote Leave's official position is that leaving the European Union would save £350m a week - a figure that has been criticised for not taking into account money which flows back to the UK from the EU.

The peer said the referendum on 23 June offered "the best opportunity in our lifetime" to leave EU which he said would "inevitably" move towards becoming "in all its essentials, a United States of Europe".

And he warned of the potential collapse of the euro - citing warnings from former Bank of England Governor Lord King.

"Every single year that the UK can put under its belt in a transition out from the EU/Eurozone reduces the chance that we in the UK will be dragged down as a result of a euro collapse," he said.

US President Barack Obama has said Britain would go to the "back of the queue" for trade deals with the US if it votes to leave the European Union while Bank of England Governor Mark Carney warned that a "technical recession" - two consecutive quarters of negative growth - was a risk.

IMF chief Christine Lagarde also joined warnings last week saying a vote to leave the EU would have "pretty bad, to very, very bad" consequences.

Lord Owen accused her of "flagrantly trying to influence the UK debate" under the chancellor's guidance and said she was "pursuing a French political agenda".

He also criticised Cabinet Secretary Sir Jeremy Heywood, suggesting he had failed in his duties by not making sure Cabinet was briefed on the risks of leaving the EU before the referendum was called.