A chapter titled “Developing the H-Bomb: An exercise in calculated Decision Making,” from the proceedings of this 2001 symposium in Stockholm, has a nice account of some of the history behind the UK’s nuclear weapons program(me).
Essentially, the chapter argues that, after deciding to build a thermonuclear weapon, the UK followed “two parallel developmental approaches.” The government tasked the Atomic Weapons Research Establishment with developing “both a fission weapon, code named Violet Club, and a two-stage design.” Despite concerns from other parts of the government, “the weapon was brought into service briefly before being replaced.” The chapter also asserts the lack of “any convincing argument” that this weapon “contributed in any significant way to the security of the UK.”
My knowledge of the British program is quite limited, so this may well be only new to me. One of my favorite parts of the chapter is its description of the risks associated with the interim weapon. The relevant part is below, but I must highlight this portion:
To minimise the possibility of an accidental explosion there was a safety device. The centre of the fissile assembly was filled with steel balls, about 1,000 pounds of them. This meant that, before an operational flight, the weapon had to be “de-balled” by a member of AWRE, and “re-balled” immediately on landing.
Former CIA Director Michael Hayden explained in this 2010 interview why the CIA chose to declassify intel concerning the Syrian reactor which Israel attacked in 2007:
You strongly advocated publicly disclosing the role intelligence played in detecting the nuclear reactor in Syria. Why did you advocate this?
It was a very complex political problem. First of all, when we became aware of it, it became very important to keep it secret. Arguably secret, because it had to be dealt with in a way that didn’t create a war in the Middle East. And the more public it became, the more difficult it would be for the Syrians to act responsibly. So no question that it needed to be kept secret.
But after a time, after the facility had been destroyed, there were two lines working—because you had two bad actors here, the Syrians and the North Koreans. With the Syrians, you needed to keep it secret, otherwise they might do something stupid if they were publicly embarrassed. With the North Koreans on the other hand, we were moving in the direction of a new arrangement with regard to things “nuclear,” including proliferation. And so, the fact that we knew the North Koreans had done this very egregious thing, I felt would undercut the confidence in the treaty when, sooner or later, it became more visible, more known, more public. So we had this line with the Syrians where you’ve got to keep it secret, but that was fading over time. Conversely, with the North Koreans, the imperative to make it public was growing over time, as we were getting to a firm agreement. I think the lines crossed about the first of the year—remember it was discovered largely in April  and destroyed in September . By about December or January , I think that’s when it’s crossed. So we at the Agency became very strong advocates for making it public. But in an intelligence process way, we knew that we had only told a few members of Congress, and the legitimacy for keeping it closely held was eroding as we got further away from the destruction of the facility, and therefore from any likely Syrian reaction. We had an additional impulse to tell Congress.