Broadcaster STV faced criticism tonight after online viewers reported problems trying to watch the head-to-head debate on Scottish independence.

While television viewers in Scotland could watch the clash between the country's First Minister Alex Salmond and former Chancellor Alistair Darling, a surge in demand online across the rest of the UK caused STV's livestream to crash.

On Twitter, STV said: "For those having problems with the STV Player at the moment we are aware of this and are working hard to fix it."

Later it added: "We're still working on fixing the live stream. The debate will be available online in full a few hours after the programme has finished."

A number of viewers expressed their frustration on Twitter.

Labour MP Diane Abbott wrote: "Finally watching #indyref debate after struggling for 40 minutes with dead STV Iplayer."

Broadcaster Andrew Neil added: "Trying to watch Salmond v Darling on STV iPlayer. But system seem overwhelmed. Any thoughts?"

Claire Stewart tweeted: "An independent Scotland needs better equipped public broadcasters. #stvcrash #ScotDecides."

Labour MP Tom Watson said: "It may not be of interest to many but you would have thought a debate on the future of the union would be broadcast UK wide."