Fitch's chief sovereign analyst, James McCormack, has told Reuters that "it is going to take some time" for the UK to get its AAA rating back.
Ratings agency Fitch followed Moody's in downgrading Britain's sovereign rating to AA+ in April.
"At the time I think that was the right call to make," McCormack told Reuters. "Projections that we were working off showed debt peaking at a level higher than we previously anticipated and further out than anticipated."
"We probably need to see medium-term projections of debt-to-GDP coming down in a sustainable way over a period of time," he said.