I suspect that with more funding the British efforts at developing a hydrogen peroxide oxidized, kerosene burning missile system for both land based and submarine launched applications could have borne fruit considerably earlier than OTL, by perhaps a decade or more.
If it had been realized earlier than OTL that the keys to storing and handling hydrogen peroxide in addition to high cleanliness of the storage vessel (suitable stainless steel alloys) were 1) achieving extremely high purity, with practically zero water content, which is counterintuitive to be sure, and 2) chilling the pure peroxide to just above its freezing point, then perhaps redoubled effort would have been made and rewarded with practical engine designs earlier, encouraged by the considerations that
1) a quasi-"hypergolic" simplicity of engine design whereby catalyzing the peroxide produces a jet of hot oxygen and steam that fuel will spontaneously combust with;
2) is coupled with substantially lower temperatures than with either hypergolic or kerosene-oxygen combustion allowing simpler, cheaper, less advanced alloys to make the engine core at given pressures;
3)the resulting propellant mix is remarkably dense, permitting storage of large reaction masses offsetting the lower specific impulse and allowing greater delta-V or throw weight for a given volume of missile;
4) although wanting to keep the peroxide at 270 -275 K or so is a sort of quasi-cryogenic requirement (with a side benefit of condensing the kerosene type fuel to be sure) it is far far easier to achieve than storing liquid oxygen at about 100 K--the difference between a typically 290 K or so exterior in summer is just 20 K (or a lot less in chilly weather in Britain) versus nearly ten times that for LOX. I envision, for a simple no-silo gantry launched version (quite vulnerable to a first strike to be sure, therefore launch-on-warning) a system whereby light fall-away gantry arms similar to the Soviet launchers for the R-7 hold pneumatic pads, essentially giant low pressure air mattressess, flushed with cold gaseous nitrogen blanketing the major length of the body of the missile that contains propellant; on launch the pads are jerked away leaving a chilled body with very high thermal inertia, even in noonday sun on the hottest summer days that happen in Britain, the sunlit side will hardly warm up all with all that chilled peroxide and kerosene touching the inner surface. Unlike the Atlas, Thor, or R-7 missiles that need to be filled with LOX at the last minute, peroxide-kerosene launchers will be filled and standing by all the time much like hypergolic missiles such as most later Soviet designs or the US Titan II; they can be launched at the push of a button any time. In fact so-called "room temperature" hypergolic rockets are just a bit oversold as such--the fact is, the N2O4 based oxidant boils at temperatures that might rarely be reached in Britain but are often exceeded in the USA in summer, whereas the hydrazine-based fuel can freeze solid at temperatures that are admittedly terribly cold even in the heartland of the USA or Alaska (or Siberia) but quite easy for an orbiting spacecraft to fall to, so that "storable" hypergol spacecraft engines need some auxiliary heating to guarantee this does not happen. The more serious problem for Earth-based missiles is of course the oxidant boiling, which is largely sidestepped by keeping the missiles in hardened bunkers that can be air-conditioned--but it is a thing and was an issue in the 1980 Damascus (Arkansas) incident where a dropped wrench socket breached the fuel tank of a Titan II missile, causing a slow but unstoppable leak that gradually weakened the partially pressure-strengthened structure predictably leading to buckling and release of the boiling hot oxidant to react with the hydrazine-laced air in the silo, eventually (after some 16 hours or so, IIRC) causing the whole missile to explode and blast out of its silo like a huge bullet--and by reading the book Command and Control that used this incident as narrative binder for a discussion of the general safety or lack thereof of American made (and presumably anyone-made) thermonuclear warheads, i learned that there was a definite possibility the H-bomb warhead might have been set off too. This did not happen to be sure, but it could have. Anyway the issue is a real one, and so is the general toxicity of both the raw oxidant and fuel substances separately and their various combustion products, which has been a real thing in terms of visible health hazards both in the former Soviet Union and ongoing Russian Republic, where Kazhak and other tribal peoples in the flight paths of Proton launches and missile tests out of Kosmograd have demonstrated cancers and other syndromes from the microscopic traces of contaminants filtering down from stratospheric and greater altitudes in the wake, and in my own, ahem, nuclear family whereby my own uncle, a SAC officer whose career largely centered on Titans, was sent down into the devastated wreck of the Damascus facility after the blow-up--he and every other member of the evaluation/clean-up team he commanded all died of the same rare and nasty cancers some decades later, himself holding out the longest but at great pain and cost. (The Air Force denies any connection but I think they are clearly lying about it in view of the universal fate of the entire squad).
I don't like hypergols much you see. I recognize that in space, they have a role, but love to see them bypassed.
And by golly, hydrogen peroxide is a suitable way to do it. In terms of immediate explosion/fire hazard the stuff is comparably risky of course, though its path of gradual decay might have enabled an ATL Ker-Peroxide Titan at Damascus to simply be drained of its oxidant and then the kerosene fuel leak patched, or drained away for the missile to be scrapped in favor of a fresh one. If one does not vent a peroxide chamber that has some catalyst introduced (and the interior cracks involved in some exterior ding such as the heavy wrench socket banging on the peroxide segment instead of the fuel segment might be a sufficient catalyst) the heat release will combine with the vapor pressure of released oxygen gas to accelerate the decomposition and eventually burst the vessel, though if the liquid is initially kept at 270 K there is a lot of heat capacity to be filled before the temperature of the peroxide can rise much, buying a lot of time, and if active cooling is required that cooling can be stepped up to check temperature rise completely or even freeze the material. One can of course include a pressure driven safety valve to vent the outgassed oxygen! To produce a Damascus incident, or the even more spectacular Soviet Nedelin Incident (which killed General Nedelin along with a hundred or so other site workers) one requires quite a lot of either stupid design failures or very unfortunate coincidences, and draining away the peroxide always seems to be possible.
But meanwhile, in terms of long term chemical toxicity--again concentrated peroxide is bad news health wise, it can do severe damage to skin, lungs, eyes etc even if its accelerant properties as a concentrated oxidant don't promote severe fires. But once dispersed, it breaks down into plain water and oxygen, and even dumped on the ground concentrated will over time decay into those substances, or reacting with various materials typically produce carbon dioxide and more water. An explosion however accomplished will drop in toxicity quite rapidly and become quite tolerable quickly, and then completely innocuous.
Of course storing tanks full of it in a submarine can be risky, but certainly less risky than storing comparable tonnages of hypergolic propellants. The USN and OTL RN, along with the French navy, eventually opted for solid fuel missiles.
It should of course be possible for the British to develop underground hardened silos just as the Americans did for both versions of Titan--the original Titan being a kerosene-oxygen rocket. As with the Titan II silo it is necessary to somehow dispose of the exhaust products as the missile rises out of the protected recess, but with ker-peroxide these products are steam and carbon dioxide, not the weird carcinogens one gets from hypergol combustion. It might be possible to actually use the exhaust to propel the missile sort of like a bullet. This approach might aid submerged launch from submarines.
Needless to say, early success, by say 1955 or so, in developing a practical IRBM comparable to say Thor, can lead to very early British space launch capability.