British aren't stupid, they wont allow any meaningful takeover, this is no take over. Such people are usually plants by the intel agencies to pacify their domestic Muslim population by creating an outwardly appearance of inclusive governance, lest it becomes apparent to their Muslim youth that they are living as second class citizens in Britain. Such token appointments serve as a means of false hope to restive populations, as something to aspire to (same with cricket recruitment). This is part of their counter-radicalization narrative building to preempt recruiters from capitalizing on Muslim isolation. They are making the Muslims feel like they have a stake in the governance of the nation, while not giving any REAL decision making power to those people. He will sit and govern the city, he doesn't get to decide foreign policy, or get oversight of intel agencies, or defense procurement or anything like that. Plumbing, roads, that is what he will do, while serving as a token 'Muslim politician'. In reality, the majority of Muslims will continue to remain in neglected ghettos while erroneously feeling that they are represented in every sphere of life, and can get there some day, if only they worked hard, like the Muslim politicians and cricketers they see on TV, who have made it big in Britain. It's done to take away their despair and give them false hope to keep them pacified.
As a country which was able to grasp the complexity of India and divide and rule for 200 years, it really isn't that difficult for Britain to manage a few Muslims in their own country by planting patriotic British Muslims who quack all the right noises to position themselves as a 'true Muslim' but have been thoroughly vetted and handled by their intel agencies. They will keep the Muslims divided to keep them from gaining any real power. The man is Muslim only in appearance, but British in his thinking (like Nehru), so the gullible followers end up accepting him as their own. This helps the intel agencies establish and extend his legitimacy. This has great propaganda value but in reality it's a British man roaming in Muslim fancy dress, if you may.
Christians are no less evil, in fact, they are far more treacherous than Muslims, it's just that their modus operandi is slick and their propaganda is polished, so we end up believing they are some sort of fluffy bunnies who could do no harm.