London police said on Wednesday they would mount an "unprecedented" operation this weekend to prevent violence and serious disorder when two large protests - anti-immigration and pro-Palestinian - take place in the British capital. At least 80,000 people are expected in London on Saturday for the two demonstrations - a pro-Palestinian march marking Nakba Day and another 'Unite the Kingdom' rally organised by the anti-Islam activist Stephen Yaxley-Lennon, better known by his pseudonym Tommy Robinson. With the football FA Cup final also being staged at Wembley in the northwest of the capital, and against a backdrop of global tensions, recent antisemitic attacks, and a raising of Britain's terrorism threat level, police said they would be using "the most assertive possible use of our powers" to forestall trouble.…