Actually, at this time there is a protest going on in London regarding oil. The ICC is afraid that sometimes the protesting people come to the stadium and spoil the pitch and ground. Due to this, the ICC has made two pitches. So that there is no obstruction in the match.
Pitch will be changed on these conditions
If the on-field umpire feels that the pitch on which the match is going on is not safe. So he can stop the match by giving this information to the match referee. If this happens, the on-field umpire and the match referee will talk to both the captains. However, if the captains do not have any problem with this, then the match will be restarted. But if this does not happen then the umpire and match referee will check whether the pitch can be repaired or not.
Along with this, he will also keep in mind that after recovering, that pitch should not become favorable for any one team. If it so happens that the pitch cannot be rectified, then the match referee ICC can talk about starting the match on another pitch. His condition will be that the second pitch should be such that a Test match can be played on it. Significantly, if the second pitch is also not fit to play then the match will be cancelled.