When is an "above Top Secret" e.g TOP SECRET ATOMIC document no longer a secret ? When it has been officially de-classified and is available via the National Archives in Kew, after say 30 or 50 years.
However to make sense of these often very technical documents, you need a lifetime of relevant expertise.
Have a look at this well researched and fascinating website, by a retired British nuclear weapons programme engineer:
Brian Burnell's British / US nuclear weapons history at http://nuclear-weapons.info
Here is an example of the sheer engineering elegance and precision which British engineers and scientists used to be capable of, over 50 years ago:
The Orange Herald spherical warhead installed in the centre section frame of a Blue Danube casing prior to the Operation Grapple tests at Christmas Island. Although smaller at approx 36 inches diameter than the Green Grass warhead of Violet Club at 45 inches, the Green Grass warhead would appear to be very similar. A notable difference would be the 72-lenses of the Green Grass implosion system, derived from the Green Bamboo design, unlike this photograph showing 32 lenses and detonators. The Blue Danube derived firing switch (the large circular item attached to the frame at top left) is clearly seen, with the firing cables leading to each detonator also clearly visible. Because the timing of the firing signal was so important, each cable was of exactly identical length, with duplicated cables to the nearest detonators having to be coiled. The nose and tail units of the casing fix to the large circular frame of the modified Blue Danube casing. Photo: MoD
Apart from the "Rubber bag full of steel ball bearings" alleged safety mechanism, some of the most powerful British weapons relied on trust in human beings, rather than technical safeguards e.g.
Strike Enabling keyset at the Bristol Aero Collection, Kemble airfield. The hexagon (Allen) key inserted into the centre of each dial to set the burst and drop conditions. The yellowish barrel-shaped object is a gripper device used to grip and remove a cover over the keyhole while wearing NBC gloves. (157) Photo: Brian Burnell.
Only one key was needed to activate the weapon preparatory to a strike.
There was no dual key system manned by two keyholders. There were no secret code numbers or secret code words. There was only one officer holding one key.
The insane logic of the nuclear arms race threw up some astonishing weapons, to specific threats (real or imagined). somehow the designers and promoters of these weapons systems (US, UK and Soviet) managed to ignore their wider practical or ethical drawbacks.:
e,g, the Davy Crockett (US) and the identical Wee Gwen (UK):
Wee Gwen was a British project name for a small, lightweight, low yield unboosted fission warhead intended for a British Army version of the US Davy Crockett close support infantry weapon. The US Army's Davy Crockett spigot mortar was available in two versions, either vehicle mounted, or a lighter model as a manpack, which broke down into three major components, each light enough to manpack. It was for use very close to the front line by the infantry, and was probably the first known use of a neutron weapon, designed to kill and incapacitate enemy troops by neutron and gamma radiation, rather than by blast and heat, although at the time the warhead was designed for use as an anti-aircraft warhead, the concept of battlefield use of neutron warheads had not yet evolved.
The W-54 warhead's small size and weight was noted by other prospective users, and it was adapted for use with the Davy Crockett spigot mortar and a manpacked ADM (Atomic Demolition Munition and landmine) both for use by the US Army.
Studies showed that in order to detonate these nuclear weapons safely, but close to friendly front-line troops, the best choice of yield was 10-20 tons. A greater yield was not especially useful, since the killing power of the weapon used against advancing enemy troops in armoured vehicles and in the open was greater by neutron and gamma emission than by the more conventional effects of heat and blast. (14) Armoured troops in particular were mostly unaffected by blast on the scale of this weapon, but armour provides little protection from radiation emissions of Wee Gwen, casualties would be unlikely to survive longer than 36 hours. Enemy troops in the open at up to 70 yards (64m) would have loss of co-ordination within one minute, be incapacitated and death would follow within 36 hours. A 10 ton yield warhead could be detonated as close as 600 yards (550m) to friendly troops.
While the weight of the fissile core is not known, and may never be known, a reasonable estimate is a minimum of 4 kg, and possibly much more.
Note that enemy troops who have received an incapacitating or lethal dose of radiation will still usually be able to fire their weapons and kill some or all of the troops being "defended" by such "frontilne" atomic weapons.
The chances of "friendly fire" or "blue on blue" casualties from such weapons which were not capable of being be accurately aimed, appear to be huge.
We suspect that the various terrorist groups who were active in the 1950's and 1960's were perfectly well aware of the potential of such devices, so the interest of al-Queada in acquiring or building such devices is nothing new, no matter what the "climate of fear" propaganda claims.
If today's terrorists did somehow manage to acquire even such a "small" fission weapon, the UK and US authorities would no doubt panic and attempt to evacuate or disrupt a vastly larger area than the "safe radius" for friendly troops specified by the designers of these weapons.