AFAIK Britain never has designed an indigenous military ICBM, Blue Streak being an IRBM. I suppose the Black Arrow project could be considered an ICBM system despite its successful use as a satellite launcher.
The UK is the only country ever to have developed an indigenous orbital space launch capability and then binned it.
I remember wandering round the old Blue Streak rocket test stands still on the range at Spade wondering what might have been...