[Reith85]

I've known it happen a couple of times, one a presenter who left a news programme for its direct rival. They weren't even let back in the building after handing in their notice.

The other worked for a facilities place in Soho, nothing particularly notable job-wise, he handed in his notice to go to a rival down the road
Immediate gardening leave, barely allowed to say goodbye to colleagues.

It happens

I'm pretty certain that in her final edition of BBC Breakfast in early 2014, hardly any reference was made to the fact that it was Susanna Reid's last appearance on the Breakfast sofa - before she began her period of "gardening leave" ahead of her transfer to ITV and Good Morning Britain.