Ofcom, the official body of the UK governing spectrum usage, says itself that as a CEPT member itself it applies the CEPT recommendation T/R 61-01, which recommends:

that CEPT member administrations recognise the principle of the CEPT radio amateur licence issued under the conditions specified in Annex 1 and Annex 2, on which the administrations of the countries visited will not levy administrative charges or spectrum fees

So, your license is accepted as long as you visit. Your nationality should make no difference.

That is very much the spirit of the cept recommendations - make it easier for people traveling, regardless of what their passport says, to do radio.

Note that you would have to check with ofcom's actual norms how that would look in detail, but come on: for this to become a problem, someone at ofcom would have to

0. Find detailed regulations surprisingly making an exception that puts visiting UK citizens at a disadvantage,
1. Look up your US call sign
2. Correlate the name they get with a UK citizenship catalog, something that they probably don't even have access to for this purpose
3. Have reasonable cause to assume that there's only one Natalie Downe between the US and UK, and that it's you
4. Cause minor problems for you

(Southern states accent) Ain't nobody got time for that, (posh English accent) to be quite honest, dear.

Ofcom, the official body of the UK governing spectrum usage, says itself that as a CEPT member itself it applies the CEPT recommendation T/R 61-01, which recommends:

that CEPT member administrations recognise the principle of the CEPT radio amateur licence issued under the conditions specified in Annex 1 and Annex 2, on which the administrations of the countries visited will not levy administrative charges or spectrum fees

So, your license is accepted as long as you visit. Your nationality should make no difference.

That is very much the spirit of the cept recommendations - make it easier for people traveling, regardless of what their passport says, to do radio.

Note that you would have to check with ofcom's actual norms how that would look in detail, but come on: for this to become a problem, someone at ofcom would have to

0. Find detailed regulations surprisingly making an exception that puts visiting UK citizens at a disadvantage,
1. Look up your US call sign
2. Correlate the name they get with a UK citizenship catalog, something that they probably don't even have access to for this purpose
3. Have reasonable cause to assume that there's only one Natalie Downe between the US and UK, and that it's you
4. Cause minor problems for you

(Southern states accent) Ain't nobody got time for that, (posh English accent) to be quite honest, dear.

Now, of course you shouldn't risk things if it can be avoided. And Hobbs seems to have found the relevant actual regulation for the UK!

It defines:

"CEPT radio amateur” means a radio amateur who holds a CEPT amateur radio licence issued by a CEPT country, other than the United Kingdom…

Note that it really makes no exceptions on the citizenship!

It says that these "CEPT radio amateurs" are exempt from requirements of UK licensing as described in "the act", which is in this case the UK radio amateur-governing law's 1(1), as found here.

To drink something long-brewed fast, that means that if any woman has a CEPT license from a nation that allows UK-licensed amateurs to do the reverse, then she won't need a UK license to operate as radio amateur in the UK.

You're fine!