Michael McIntyre was there - as has been noted
Rumour/theory in later years, after he became famous and this clip started getting posted, was that he engineered it, had his friend ring up to do this on that day when he was in the audience.
This has never been proven or admitted to, though it does make a great story, urban myth.
And, if he wasn't behind it, it could be viewed as quite a coincidence that it occurred on the day he "just happened" to be sitting right there.
Eliot: "I want to ask Five Star why they're so fucking crap"
Sarah: "OK, well let's ask Steadman - why are Five Star so fucking crap?"