[TV Insider]

The BBC, Sky and ITN all have their Westminster offices and studios in 4 Millbank. 

It's also home to facilities companies used by other broadcasters whenever they needed crews or studios at Westminster. At one point this was Millbank Studios owned by ITV but I'm not sure what the situation is now. In fact for a long time BBC Parliament was played out of Millbank Studios by ITV employees

LBC also have a studio at 4 Millbank.

4 Millbank is also 1 minute away from College Green, which is also sometimes used for the morning round. Most broadcasters have permanent circuits here. The new GB News studio is 8 minutes away from the other broadcasters, so I suspect that they will still have to use College Green.

Both GB News and TalkTV used Victoria Tower Gardens this morning, which is also 1 minute away from 4 Millbank.