How hard is it to do a fab job of playing a Beatle?

Playing any well-known figure from recent history is a challenge, but the challenge of finding four actors to put in convincing portrayals of four of the most famous people in popular culture is one not many directors have attempted.

Earlier this month, director Sam Mendes announced the cast for his four-part Beatles biopic, with each member of the band set to be the subject of their own feature-length films set for release in 2028.

Actors Harris Dickinson, Paul Mescal, Joseph Quinn and Barry Keoghan will play John Lennon, Paul McCartney, George Harrison and Ringo Starr respectively.

Their performances – and particularly their efforts at the Beatles' distinctive accents – will be closely watched by fans the world over. And if previous actors' attempts are anything to go by, they should brace themselves for some serious scrutiny.

Perhaps one of the most famous and successful Beatles biopics is 1994's Backbeat, set in the band's 1960-1962 Hamburg era.

On the one hand, it had Liverpool actor Ian Hart turning in a convincing Lennon (even if he was not exactly Lennon's double).

But on the other, Hollywood actor Stephen Dorff, playing the film's lead character of original Beatles bass player and artist Stuart Sutcliffe, who died of a brain haemorrhage aged just 21, provided an uncanny likeness. But his attempt at the Liverpool accent has received, over the years since, reviews from "decent" to "variable" to "awful".

So should any actor taking on a Beatle role be wary?

Beatles historian Paul Du Noyer, who wrote The Beatles: The Complete Illustrated Story and Conversations With Paul McCartney, said: "The Beatles are so well known to us all, not just their faces but every nuance of the way they talk, every mannerism.

"Many of us know the Beatles as well as we know our own families. It can be difficult for us to suspend the disbelief.

"Even when I've seen performances that were very good, for example Ian Hart in Backbeat, that got around the problem of the familiarity by dwelling on a lesser-known period of their story."

Du Noyer added that some Beatles might seem easier to take off than others.

"In some ways, you stick a wig and a beard on someone, little round granny glasses and a white suit and everyone goes, 'It's John Lennon'"

But he said McCartney was a tougher portrayal to nail – especially when the man himself is a tough critic.

"Paul has been very critical of films like [Sam Taylor-Wood's early years biopic of John Lennon] Nowhere Boy, and Backbeat, because they tend to fall into a pastiche of McCartney that he doesn't recognise – he doesn't like the stereotype of him being the cute one, the manipulative one."

So does Sam Mendes have a job on his hands?

Du Noyer added: "He's got bankable stars, who won't let themselves down. I know there's been some disappointment among Liverpudlians because non-Liverpudlians have been cast in the roles, but even as a loyal Liverpudlian I can't condemn Sam Mendes on the casting, because he is making films for the whole world to watch.

"I think the accuracy of the Liverpool accent will be pretty low down the list of things he needs to cover."

Edda Sharpe, a Merseyside-based voice and dialect coach who has worked with actors at the Royal Shakespeare Company and the National Theatre, said there were some specific challenges to taking on the voice of a Beatle.

Among them is the fact that the accent with which John, Paul, George and Ringo spoke is much less pronounced than the one many might associate with Liverpool today.

Beatles aficionados will know that on the Let It Be album version of the old Liverpool folk tune Maggie May, Lennon deliberately exaggerated the Liverpool accent, elongating his vowels and adding a much more nasal quality to it.

The performance has more in common with today's Scouse accent than it did with the one the Beatles spoke with.

"And the challenge is, the way the Beatles spoke, you just don't hear that any more. It's a completely different tone to the Liverpool accent we are currently exposed to," Sharpe said.

"And you are not just trying to create the sound of someone from Liverpool in the 1960s, you are trying to create the sound of people that everyone is familiar with."

She said there might be advantages for Irish actors Mescal and Keoghan, as there are certain common traits to both Liverpool and Irish accents.

But she said similarities in accent could also prove problematic for actors.

"The northern Irish accent, particularly, has this sort of down-and-then-up quality, and when you listen to early recordings of the Beatles you hear what sounds like a familiar Irish pattern.

"But sometimes accents that are closer to your own are harder to do than ones that are completely different."

Dr Paul Cooper, a senior lecturer in English Language at the University of Liverpool, said there was academic research to back up the idea that "Scouse was getting more Scouse" than it used to be in the time of the Beatles.

He said research by linguistics expert Marten Juskan into the changing sound of the Scouse accent supported the claim.

"Also," said Cooper, "I think younger people are now looking at the accent more favourably than maybe it was looked at 30 or 40 years ago.

"There's always been a strong sense of pride in the accent, but I think in the 1980s and 1990s you got the Harry Enfield Scousers stuff and it maybe became viewed a bit more negatively.

"I think now it's viewed a bit more favourably again. Plus, Liverpool is much more of a tourist destination now, and the accent is thought of as very welcoming and very friendly."

But what does an actor who has taken on not one but two Beatle roles think the challenge will be for the actors taking on the Fab Four in Mendes' films?

Michael Hawkins played John Lennon in the successful stage show Cilla: The Musical based on the life and career of Liverpool entertainer Cilla Black, and, in his first TV role, George Harrison in the 2014 ITV serial biopic Cilla, with Sheridan Smith taking the title role.

Hawkins said: "You've got to do your research, watch as much stuff as you can.

"Obviously in the films like Hard Days Night they're sort of playing a version of themselves, but with the Get Back film, you see more of them as how they were.

"So many people feel like they know them so well that if you get something a little off, it'll make people wince.

"It's about getting the authenticity, and not doing a caricature."

The 35-year-old, a member of "parody band" Ugly Baby, said even as a born-and-bred Scouser he was not immune from scrutiny for his portrayal of Harrison in Cilla.

He added: "I didn't really change my accent much for playing George. And then one of my mates sent me a review, from the Mirror, I think it was, where they were saying George's accent was just a general northern one, with no hint of the 'Pool.

"And I was the only Scouser out of the four of us."