European football's governing body, UEFA, is opposed to three-nation bids for the expanded 2016 European championships, Reuters reports.
According to the news service, UEFA said that it would permit solo bids and joint bids by two neighbouring national associations, but that bids involving three or more countries would be considered "under exceptional circumstances" only.
The announcement follows media reports last week that Scotland, Wales and Northern Ireland had held preliminary talks about a joint bid.
General secretary David Taylor told reporters that the full bidding regulations were still to be finalised but that potential bidders should be prepared to make at least nine stadiums available.
"It is our view that nine stadiums will be expected for 2016, possibly with some additional back-up stadiums," Taylor said, whilst UEFA's competitions director Giorgio Marchetti added that bidders would be expected to provide stadiums with capacities ranging between 30,000 to 50,000 spectators, including "at least a couple" holding 50,000 or more.
UEFA decided at its last executive committee meeting in September to increase the size of the championships, starting with the 2016 edition, from 16 to 24 teams. Member associations will be formally invited to express bidding interests in an initial phase running from December 15 to March 9, 2009, with a final decision due to be announced in May 2010.
