When I applied this morning, at the point of initiating the switch I was offered a full or partial switch. The former closes the old account and moves all debits etc, plus sets up account forwarding; the latter enables you to pick and choose what gets moved, and leaves the old account open.
All that said, the Ts & Cs are particularly clear - the very first sentence is:
Originally Posted by Barclays
You can collect 25,000 Avios when you complete a full current account switch
Unfortunately, I neglected to read further to where it says:
Originally Posted by Barclays
This offer is only available to those who were British Airways Executive Club Members before 22 October 2019 and received the original offer email.
I did not receive the email, but my partner did. I've initiated the full switch, and now expect to receive nothing. Never mind.