UPDATE 1-UK says second Brexit vote would take over a year to organise - source

A second referendum on Britain's membership of the European Union would take more than a year to organise, according to official government guidance shown to lawmakers on Wednesday, a source in Prime Minister Theresa May's office said.

Earlier, a spokeswoman for May told reporters that a one-page document had been shown to lawmakers during meetings aimed at finding a way forward on Brexit.

"In order to inform the discussions, a very short paper set out in factual detail the number of months that would be required, this was illustrative only and our position of course is that there will be no second referendum," she said.

May has been meeting lawmakers from all parties on Thursday in an attempt to find a way out of an impasse over how Britain should leave the EU, after May's own plan was resoundingly rejected by parliament on Tuesday.

Although May has repeatedly rejected a second referendum, a vocal campaign in favour of holding a new vote has the support of some lawmakers.

(Reporting by Kylie MacLellan and William James. Editing by Andrew MacAskill)