[JMT1985]

For what it's worth, today's national bulletins have also been coming from the lower, ITV News London desk

Well, it could be they are changing the desk - as since both desks face opposite each other, and are very close together, not using the larger desk doesn't make sense, as it is not really "cost effective" to just air from the small desk, as they are in the same studio. 

So using logic, it seems they must be trying out a new desk or fixing a problem with the larger desk