The trivia items below may give away important plot points.
A subtle hint that President James Heller isn't dead may be the clock in the end: there are sounds as the last 4 seconds count away. In 24 (2001), the death of an important ally to Jack in the last scene of an episode was always accompanied by a silent clock.
When Bauer and Heller are travelling towards Wembley stadium by helicopter, there is an aerial shot of the helicopter flying over London, along the Thames river and over Tower Bridge. The helicopter is actually flying the wrong way, as they are travelling East whereas Wembley is located in North Weat London (the other direction).