On the face of it, that's the reason behind their cancellation, but that decision was made by a government that also claimed that a developed country needs a thriving aviation industry! Sadly however, that the projects got to a point that they became unaffordable by the nation in the first place is what muddies the waters a little. Politics, bad timing, over engineering, inter-service disputes, money worries, technical issues, overhaul of the aviation industry - all conspired to increase cost and reduce productivity on all the projects. As it was, the British aircraft would have been superior in capability compared to their American substitutes, although the F-4 could carry a bigger load and was faster than what the P.1154 was projected to be, it had its V/STOL capability, which would have proved more versatile as a carrier aircraft - see Sea Harrier carrier operations during the Falklands for evidence of this.
It's also worth remembering that the Brits had a few other aerospace projects on the go at the time, chief of which was the Concorde, although the government wanted to get out of that too, but they had signed a binding contract and couldn't. There was also the European Launcher Development Organisation, or ELDO;
https://en.wikipedia.org/wiki/European_Launcher_Development_Organisation
Britain lost interest and withdrew funding and support after the Europa rocket kept failing. On only one occasion was a failure attributed to the British component (the Blue Streak first stage), on one flight, the fuel inside the Blue Streak was sloshing about so much that it destabilised the gyros and the rocket had to be destroyed in flight.
https://en.wikipedia.org/wiki/Europa_(rocket)
Britain also had its own indigenous satellite launcher, the Black Arrow;
https://en.wikipedia.org/wiki/Black_Arrow although it only ever launched one satellite.
After this, the British realised that space was too expensive and that Britain didn't
need a space programme, so stopped building rockets and rocket motors, which it had done so since the end of WW2.