ITV will broadcast the election debate live online and allow viewers to send their comments in real-time via its website.

Millions are expected to tune into ITV1 tonight at 8.30 pm to watch the UK’s first live televised election debate between the leaders of the three main political parties.

Besides the televised coverage and live video stream of the debate on its website, the broadcaster will allow users to send comments and questions via Twitter and live chat. It will also include an interactive poll to show how party leaders are faring.

Users will also be able to catch up with any part of the debate they missed on the ITV Player and the ITV1 YouTube channel in the UK and internationally.

Three election debates will take place with the next two to be televised on Sky and the BBC. ITV is not the only broadcaster to be using interactive technologies to get an overview of viewers' reactions. Sky will be using SMS messaging to gauge audience reaction to all the debates and will put graphs on its website.

Alastair Stewart will moderate the panel tonight. To gauge a general reaction, ITV has picked a focus group and the broadcaster will use a tool called The Worm to show how each leader is faring.

This tool will create a live 'worm graph' that will be displayed on the live-video stream to show approval, disapproval or neutral feelings from the focus group.

During and after the debate, the website will also host a live, real-time, online chat so people can submit their thoughts and views on key quotes from C ameron, Brown and Clegg.

ITV News correspondents and political experts will also be on hand to answer questions from people using the tool and also give their reactions to the debate.

The broadcaster is also using social-networking sites to broaden the response. Facebook users can post updates through the ITV website and see what other Facebook are saying.

A Twitter tracker will tally reactions to the leaders' performances throughout the debate, in real-time by following the posts of 5,000 hand-picked Twitter users. Leaders are ranked on a 'sentiment' scale of one to five.

Another tool will highlight the most frequently used words and phrases throughout the debate.