Guess Ernie isn’t speculating or basing his information on the internet drivel? One thing I’m sure of is that HM government always, rightly, refuses to discuss how the nuclear deterrent works. We don’t have air delivered weapons or tactical battlefield weapons now either. 2006 white paper https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/27378/DefenceWhitePaper2006_Cm6994.pdf
Page 23, para 4.6
The UK’s current nuclear deterrent is fully operationally independent of the US:
• decision-making and use of the system remains entirely sovereign to the UK;
• only the Prime Minister can authorise the use of the UK’s nuclear deterrent, even if the missiles are to be fired as part of a NATO response;
• the instruction to fire would be transmitted to the submarine using only UK codes and UK equipment;
• all the command and control procedures are fully independent; and
• the Vanguard-class submarines can operate readily without the Global Positioning by Satellite (GPS) system and the Trident D5 missile does not use GPS at all: it has an inertial guidance system. There is nothing in the planned Trident D5 life extension programme that will change this position.
Guess Ernie didn’t believe HM government, you did read this before posting guys?