The geography of the UK isn't really suitable for space launches. You want to launch eastwards to benefit from the rotation of the Earth, and (unless you're China) you don't want to launch over land in case your rocket fails. Launch sites further south might also be preferable as they have better access to low inclination orbits (though for polar orbits you'd prefer northern launch sites). There's no good location in the UK that satisfies all these. Btw, the US does most of its launches from Floria for much the same reasons.