Treasury minister Danny Alexander said the EU was "one of the central pillars of British prosperity and security".
"Membership of the EU gives market access to British firms, makes us more attractive to overseas investors, and underpins more than three million British jobs," he said.
"EU trade deals with the US, India, Canada and Japan will be worth billions to the UK economy but could not be won by the UK alone."
"Britain must work with our allies for change from within to ensure the EU continues to take reform seriously.
"The isolationists are reckless with our prosperity and security. We cannot let them succeed."
More top news
Sir Nicholas Winton, who rescued 669 children from the Nazis, didn't tell anyone about his exploits for 50 years - not even his wife.
Police believe one of the West's most infamous criminals, timeshare fraudster John Palmer, was murdered.
Police say a 'disaster was averted' when officers caught a suspected drink-driver who tried to drive the wrong way up the M6.