I have a feeling Plunkett, and once Hoggard is out, Harmison may have a slog tomorrow morning, and look to push the lead onto 350+ in the first half-hour. That would give Pakistan about 80 overs to score 350 - game on.
I think the Sky commentators had a valid point with reference to Nagpur. If Pakistan were to push along at about 3-3.5 an over, even until a fair way into the evening session, then England could be in trouble. Channel in the Afridi factor and England should be scared.
Having said that if Butt, Farhat and Iqbal all go within the first 20 overs, and Inzamam/Yousuf fall fairly early on, England will be confident of victory.
In other words, the whole fate of the Test lies on the performances of the Pakistani top three vs Harmison, Hoggard and Plunkett.