By Steve Keating SILVERSTONE, England (Reuters) – British police said they have credible intelligence a group of protesters are planning to disrupt the Grand Prix at Silverstone this weekend and issued a pre-emptive warning on Friday by telling them not to put themselves or drivers at risk. With a record three-day attendance of 400,000 expected to descend on the circuit 90 minutes outside London, the race is one of the British summer’s sporting highlights and has in the past been a magnet for protesters. Two years ago police arrested four people after protestors displayed a banner for climate …