Re: Answer is simple
Lets follow your logic?
A quick google shows we pay into the ESA 374 million a year.
So in your make believe world where does the funding come from for a purely UK space agency? If we do it on our own, where does it come from in a cash starved UK economy that is a shadow of its former self.
The ESA budget per year is around 6 billion (remember we pay in 374 million). https://www.esa.int/About_Us/Corporate_news/Funding
Do we cut Health, Defence, Benefits, what about the pensions? Education? Bearing in mind we need to buy the rockets or build them, find a space port near the equator, pay the country to let us launch rockets from their land like the ESA does, open a technology centre, recruit the scientists and all the other expensive stuff that the ESA currently do.
Lets look at JUST the Galileo GPS system which apparently was 10 Billion?
So in your world lets cut defence to pay for it. Our defence budget is 39 billion, from 2019 numbers. So we take 25% off defence to pay for your UK GPS system. What do we lose? Both aircraft carriers or a couple of submarines? All of the RAF?
Benefits? The largest state benefit is the pension which was 96 billion in 2019. So every pensioner takes 10% pay cut for your space GPS system (lets not count all the other required stuff like rockets and staff).
Education, how many school and teachers take up 10 billion from the education budget of 89 billion?
No amount of bravery and happy clapping will cover the fact that doing it on our own is too expensive and budgets need to be cut somewhere to pay for it.
Brexit supporters really don't get it. All bluster with no real look at the finances involved when 28 countries pay in together versus doing it alone.