They might very well want a muslim world, where we all behead each other etc.. But in reality most people just want to get on with there day to day lives and have no time for nonsensical things like religion, of the muzzies I know none of them pray 7 times a day etc, just like us Christians only ever go to church for funerals and weddings.
I think you're making the mistake that many do when they compare Islam to Christianity.
The average Muslim is not as lapsed in their faith as the average Western Christian. If they were, we would not have countless of their adherents willing to commit acts of violence and die for it.
Muslims tend to take their religion very seriously even if many don't follow all the required tenants. Many of them are as religious as Christian Europeans were several centuries ago. That itself is a frightening thought - that large communities with a medieval mindset are living in 21st century Britain.
As the Muslim population grows in the UK, the fundamentalist Salafi movement grows with it. I'm concerned that as Muslim numbers continue to expand, they will become increasingly cliquish and start to develop a "groupthink" mentality which will veer more towards Islamic literalism (Bi-la kaifa) than Islamic modernism.
Do I think that the UK will eventually see Muslims forcibly enforcing Sharia nationwide across the streets? No.
However, I do see the UK becoming increasingly fragmented and divided as a society.
Nations are created by those within it sharing similar values, ideas and identity. If these similarities evaporate, than a nation may not stay united for long.