LONDON, May 15 (Reuters) - Scottish nationalists may defy British Prime Minister David Cameron if he refuses to give them another independence referendum, an unidentified Scottish National Party source was quoted as saying by The Times newspaper on Friday.
Scots voted 55-45 percent to reject independence in a Sept. 18 referendum last year, but spectacular gains by Scottish nationalists in last week's general election have stoked calls among supporters of a breakaway for a second independence vote.
Cameron on Sunday ruled out that option, but Scottish National Party (SNP) leader Nicola Sturgeon has said Cameron does not have the right to refuse a vote.
The Times and the Guardian newspapers quoted an unidentified senior SNP source in London as saying that the party would be prepared hold an indicative ballot of the Scottish people if it thought it had a political mandate for a referendum.
"It only has to be once," the unidentified source was quoted as saying by The Times.
Cameron and Sturgeon are due to meet in Scotland on Friday.
Sturgeon, who supports independence, has given conflicting signals about whether she would pledge another independence referendum as part of her manifesto for a parliamentary election in Scotland in 2016. (Reporting by Guy Faulconbridge; Editing by Andrew Osborn)