There are plans to build a massive new mosque in the east end of London - on or around the site of the new Olympic village, I believe - that will supposedly accommodate some 70,000 Muslims. I don't think this should be allowed - at least, not until every other faith has the same right to build places of worship in ALL muslim countries.
Some might argue that if we don't let them build mosques here, why should they let Christians build churches in Saudi Arabia? Well, we've been letting them build mosques in Britain for years and they have yet to reciprocate in muslim countries. In fact, it's getting harder to even maintain what churches there are (which are frequently subjected to attack - by Muslims). It is my belief that Islam will not reform until they are forced to - and they will not be forced if we keep giving in to the ever increasing demands of the muslim population. By banning the building of mosques (and refusing to grant other privileges to Muslims that are not reciprocated in Muslims countries) you will put the onus on moderate Muslims - if they really exist - to put pressure on muslim countries to grant other, non-muslim faiths, the same rights and privileges they demand in Christian countries.
In the meantime Muslims can use existing mosques or pray at home. When Saudi allows Christians to build a cathedral in Mecca, then British Muslims can have their 70,000 kneeler mosque.
Update: 10:56 26/09/2006
Via Melanie Phillips, I came across an article in The Telegraph by Philip Johnstone who reports that making way for the new Olympic stadium and the mega-mosque (the largest in Europe apparently) will be Europes largest evangelical church - the Kingsway International Christian Centre - with 12,000 worshippers on a Sunday. So we're not just allowing more and ever larger mosques to be built, we're actually demolishing our own churches to make way for mosques!
Shall we just be done with it and become an Islamic Republic now?