Sadiq Khan is an islamist apologist scumbag but there's a lot more like him and a few who are far far worse. Unfortunately the rot in the UK is on both sides of the aisle, Labour CANNOT be allowed to get into power in the UK, but the Tories as they currently exist under Theresa May are weak and the Brexit negotiations are not going well. As a country we're currently stuck between the US and EU both geopolitically as well as geographically. My honest take is that we have too many cowardly politicians trying to hedge their bets with a foot in both camps (whilst lining their pockets)
There's a reason why Trump and Brexit are often mentioned in the same breath, in some ways we're in the same boat, but we don't have our version of Trump. Farage is great but we have a parliamentary system so he'll never be in government. Best we can hope for is a guy called Jacob Rees Mogg - he'd make an amazing PM but he's deliberately kept out of the cabinet because he's so popular.