From "Nuclear Deterrent" to First Strike. Has UK policy changed?

It has always in my memory at least  that "British Nuclear Deterrent "are words that  always  have gone together and even if I didn't agree with it I could  at least accept it as ab honest argument.

As this changed? 

When Jeremy Corbyn was heckled by a live TV audience as he repeatedly refused to say if he would fire Britain’s Trident missiles if the country was under “imminent threat from nuclear weapons” in what seemed a coordinated  attack on question time , there seemed to be no mainstream questioning of whether we are to use first strike  of Nuclear Weapons  

According to the independent 

The Labour leader had his most uncomfortable moment of the election campaign after he claimed he would deal with the threat “earlier by negotiation and talks”.
One questioner said: “I find it incredibly concerning that you wouldn’t ever commit to doing that. It’s our safety that you have to look out for first and foremost.”
A second said: “Would you allow North Korea or some idiot in Iran to bomb us and then say ‘ooh, we’d better start talking’? You would be too late.”
Mr Corbyn was accused by BBC presenter David Dimbleby of “dodging the question” and of thinking about an “ideal” situation” – rather than of the stark “reality” of nuclear threat.
Ruling out “first use” of Trident, the Labour leader said: “I would do everything I can to ensure that any threat is actually dealt with earlier on by negotiations and talks
“The idea of anyone ever using a nuclear weapon anywhere in the world is utterly appalling and terrible.”
Asked if he never fire Trident “under any circumstances”, Mr Corbyn replied: “The most effective use of it is not to use it, because it’s there.”

The thing that stood out is the fact that some people be even gleeful of a UK )but they probably mean US)Nuclear attack killing millions of innocent  civilians..

Even if you considered Mr Corbyn saying he would not retaliate with nuclear Weapons  it is probably the real view of most of our Prime Ministers unless they were insane.

The letters of last resort are four identically-worded handwritten letters from the Prime Minister of the United Kingdom to the commanding officers of the four British ballistic missile submarines. They contain orders on what action to take in the event that an enemy nuclear strike has destroyed the British government and has killed or otherwise incapacitated both the Prime Minister and the "second person" (normally a high-ranking member of the Cabinet) whom the Prime Minister has designated to make a decision on how to act in the event of the Prime Minister's death. In the event that the orders were to be carried out, the action taken could be the last official act of Her Majesty's Government.

According to Peter Hennessy's book The Secret State: Whitehall and the Cold War, 1945 to 1970, the process by which a Vanguard-class submarine commander would determine if the British government continues to function includes, amongst other checks, establishing whether BBC Radio 4 continues broadcasting.^[8]

In 1983, the procedure for Polaris submarines was to open the envelopes if there was an evident nuclear attack, or if all UK naval broadcasts had ceased for four hours.

While the contents of these letters are secret, according to the December 2008 BBC Radio 4 documentary The Human Button, there were four known options given to the Prime Minister to include in the letters. The Prime Minister instructs the submarine commander to:

1. retaliate with nuclear weapons;
2. not retaliate;
3. use their own judgement; or
4. place the submarine under an allied country's command, if possible. The documentary mentions Australia and the United States.

The Guardian reported in 2016 that the options are said to include: "Put yourself under the command of the US, if it is still there", "Go to Australia", "Retaliate", or "Use your own judgement".

Corbyn may be the first Prime Minister to publicly rule  out the first first option . but the consensus is that so would have had most if not all his predecessors.

However what seem to have changed is that some politicians are  prepared to even take the option that is not there and order a first strike.

Speaking to BBC Radio Four’s Today programme, in Apri degence Secretary Michael Fallonn said voters tempted by Labour had been left “completely unsure as to wat would actually happen to our nuclear deterrent”.

But he went further, marking out a clear divide between the parties when asked if Ms May was ready to use Trident as a “pre-emptive initial strike”.

“In the most extreme circumstances, we have made it very clear that you can’t rule out the use of nuclear weapons as a first strike,

Asked in what circumstances, he replied:

 “They are better not specified or described, which would only give comfort to our enemies and make the deterrent less credible.
“The whole point about the deterrent is that you have got to leave uncertainty in the mind of anyone who might be thinking of using weapons against this country.”

How  have we  gone from a British  Nuclear Deterrent  deterrence " which we probably (and the rest of the world knew) would not to use . To  what looks like an organised  group of men in audience cheering  a call for mass slaughter, which  the Tories and alas some Labour Politicians seem to  endorse as a policy.?