Rhetorical, right now, I guess...
Which "ATC" was supposed to know that Elstree was not available? ATC could not "direct him to Battersea". ATC cannot order the diversion of an aircraft; that is wholly the pilot's responsibility.
We'll all be interested to learn whether the pilot had declared an emergency, or asked for urgent assistance from the ground. If not, either the pilot was unaware of any imminent danger, or deemed it impracticable for ground to assist; a pilot of his experience might justifiably decide that's the best if he does not have a copilot to assist and the immediate problem needs 100% flying concentration not RT conversation. Or chose not to.
I rather suspect that by now we'd have been told had the pilot declared a mechanical or other problem and those with many years experience will be forming ideas.