I would imagine that both HMG and HM himself are feeling somewhat uncomfortable about what Trump might do during his state visit in September.
His press conference on Monday was bad enough, giving Starmer (and his wife Victoria) the benefit of his views on what the UK should do about, among other things, immigration, wind farms and North Sea oil, and also what he thinks of the Mayor of London.
During his state visit, however, he'll be appearing not alongside the PM but at formal occasions alongside the king himself. For example, at the state banquet, he'll be replying to the king's speech and toast, and proposing a toast of his own.
The speeches are supposed to be non-contentious, but that's never stopped Trump before, and if he gets bored with his prepared speech and starts free associating to Charles about immigration to the UK and about wind farms with the cameras running, it's going to be pretty painful.