No the Bank of England Governor could shut down the banking system, refuse to fund Government debt and bring down this Govt. The civil service can passivley or activley refuse to carry out Ministers orders, the Armed Forces can refuse to fight and the Police can refuse to enforce law. All of tthese people swear allegiance to the Queen and not the Govt of the day.
Look who met the Queen on 26 March 2009.
Mr. Mervyn King (Governor of the Bank of England) was received by Her Majesty.
Air Chief Marshal Sir Jock Stirrup (Chief of the Defence Staff) was received by The Queen.