Azerbaijan, the source claims, tried to buy high scores from jury members with "enough money to live off for a year".
Azerbaijan's Farid Mammadov was awarded 234 votes and was runner-up to Denmark's Emmelie de Forest, who triumphed with 281. According to the reports, other delegations tried to set up vote-swapping schemes a week before the semi-final.
The unnamed delegate also claimed to have received a phone call from a southern European delegate who wanted to buy votes in return for positive PR coverage of their country's act.
The source claimed that the EBU had shown no interest in investigating the claims, despite being told about them last May.
But the EBU insists it is taking the claims seriously. Sietse Bakker, the event's supervisor, confirmed that Azerbaijan is under investigation.
The UK's entrant, Bonnie Tyler, who came 19th, earlier told a French newspaper that she overheard Russians "complaining to Azerbaijan: 'Why didn't you give us the points we paid for?'"
Azerbaijan has already been accused of trying to pay Lithuanian students to vote multiple times. A recording showing teenagers being offered cash was published on the day of the Eurovision final in May by the Lithuanian website 15min.
Mr Bakker said: "It is interesting that this 'anonymous' delegate claims we are not interested in investigating this, or taking action, while in fact we have been doing so and have been very open about it."
He dismissed separate claims made against Macedonia, referring to "speculation without any foundation".
It is not the first time the song contest has been linked to vote-rigging. In 1968 Cliff Richard was believed to have been robbed of victory by General Franco's regime; the Spanish act Massiel won with La La La and a one-point lead.
A documentary by Montse Fernandez Vila, released in 2008, claims the win was due to a fix cooked up by TV executives at Spain's state-run channel.
- The Independent
