Could you please point me to the laws in the UK that allow the government to prohibit the building of mosques?
If the UK legal system is similar to that in the US, there should be all sorts of laws at every level of government that can be used to stop (or prosecute) just about anything/anyone. There's zoning, environmental, taxation, continuing criminal enterprise, civil rights, etc. etc. etc. If not, one can always get an appropriate law passed if the legislative body is "properly" motivated.