Not reasonable unless the proper security/privacy guarantees are in place. Otherwise this risks a massive security vulnerability; what kind of information is being shared with ChatGPT?
Based on the disclosure here, he's not sharing any information. He's doing research, asking questions, a perfectly reasonable use of the tool. Not unlike using Google.
I'm sure if he wasn't already aware, he's been briefed by his SpAd or civil servant (possibly via the security services) not to disclose any sensitive information.
It's a lot like using Google, but it's different in at least one important way: it doesn't reveal where the information comes from. How do you know if ChatGPT is repeating The New York Times, reddit, or 4chan?
I'm sure if he wasn't already aware, he's been briefed by his SpAd or civil servant (possibly via the security services) not to disclose any sensitive information.