Blue Streak was a large ICBM built by the British government around 1960. Although technically successful within the bounds of the design, it was immediately cancelled due to its reliance on cryogenic liquid oxygen. This choice of fuel meant that by the time it could be fuelled for firing, enemy nuclear missiles would have destroyed the launch pad; and the fuel would evaporate if left in the vehicle. Ironically, all the other British launchers used the very slightly less powerful, but more storeable, hydrogen peroxide as an oxidiser, and careful design could have allowed that to be used; but the design for Blue Streak used the American technology of liquid oxygen instead, a critical mistake.

Modern ICBMs use 'storeable propellents' which can be left in the vehicle for years; but they are highly toxic.

The other point is that the British government simply ran out of money. After the end of WWII the UK was practically bankrupt, and it took decades to recover. 1965 was the point where the government fully understood that the UK was no longer a world power in the sense it had been at the turn of the century. Britain simply could not afford space activities at that time, as there was no market, and Blue Streak made no sense as an ICBM.

Essentially the Rolls Royce engineers that built it wanted to go into space, and they were quite capable of designing something to do that; perhaps more so than NASA or Russia at that time. Noteably, Black Knight could have been fitted on top of the vehicle to place payload into GEO orbit- but no geosynchronous satellites existed at the time, and so the decision to cancel it was made. Only a handful of years later, with 20-20 hindsight, the decision turned out to be a mistake, as geosynchronous telecommunications satellites started to appear.