LONDON - Scotland's leader Alex Salmond says a campaign for independence will be launched in May, more than two years before the preferred date for a referendum on leaving the United Kingdom.

Salmond is seeking to hold an independence referendum in September 2014, hoping that a separation from London would be completed with a May 2016 election for the Scottish Parliament.

He told the BBC on Sunday he is "so confident" of winning the referendum that he wants a long "yes" campaign period to ensure voters in Scotland have answers to all their questions about its implications.

Opinion polls show that only about a third of Scots favour splitting up the nation, and Britain's Prime Minister David Cameron is pressing for the independence vote to be held before 2014.