Do I have to declare a U grade that I RESAT and got an A in?

As usual, there is a disconnect between what UCAS says in its guidance and the declaration you are required to make when you submit your application, and the advice you get from their helpdesk people.

Declare it, is my advice, but it is up to you.

My two penn'orthworth

The UCAS helpline may have misunderstood what the OP was saying.

UCAS might have thought that she was asking about a resat module within a qualification (as was possible until very recently) rather than a resat qualification

I contacted UCAS and I can confirm that I do NOT have to declare Us for qualifications I resat.

I contacted UCAS and I can confirm that I do NOT have to declare Us for qualifications I resat.

Oh so are UCAS lying on their website? Either they are, you didn't call or the adviser you spoke to doesn't know what they're talking about.

Previous experience makes the last of those three options the most likely, unfortunately.

https://www.ucas.com/corporate/join-our-team/job-vacancies/team-manager

But look at the salary for a managerial position. There are several retail management positions in Cheltenham paying more.

Yes you do - UCAS makes it very clear before sending off applications that everything, including Us, has to be declared. OP's situation is a little different, but otherwise people should always declare every grade they get, from Us to A*s.