Such a venture could cost, at a conservative estimate, around 500 billion pounds. That's around £8000 for every man, woman and child in the UK. Other than prestige why would we want to do it ? Such a venture would almost certainly involve international collaboration anyway.
Has there been an entirely British aeronautical/aviation venture since the Vickers VC-10 airliner ? If a privately-funded British satellite needs to be launched then there are competitively-priced launch vehicles already out there.
Even the doomed Beagle mission to Mars got a piggy-back !
Our contribution to ESA is only a miserly 6%.