It was raining lightly at the time.
The officer was on a security detail. He is a member of the police department of Strathclyde, a nearby town, McClellan said.
The
president was concerned about the officer's condition, and talked with
him for some time after the collision, McClellan said. The president
also asked White House physician Richard Tubb to monitor the officer's
condition at the hospital.
The fall did not affect the
president's schedule. Dressed in a tuxedo, he attended a dinner hosted
by Queen Elizabeth at the annual Group of Eight economic summit. He
showed no signs of distress. (link)