[alternative-answer]

MP's aren't paid to question things, they know if they did not tow the official party line that the biggest weapon anyone has to destroy their reputation is character assination, they'll dig up the dirt on them, (the dirt they were encouraged to get involved in in the first place that seemed OK at the time and were reassured that it was all in their best interests) and destroy their politial career and personal life. Keep em in line with fear and they'll do, not do and say anything.