London police braced for their busiest day in years on Saturday, when tens of thousands of protesters were expected to attend the latest rally staged by far-right activist Tommy Robinson.The British capital's Metropolitan Police said it would deploy 4,000 officers -- alongside horses, dogs, drones and helicopters -- to manage the march and a counter-demonstration merged with a pro-Palestinian protest, as well as the FA Cup final.The Met has imposed various conditions on the two rallies, over their routes and timings, in a bid to keep rival attendees apart.The force, which estimates the operation will cost £4.5 million ($6 million),...