The actor had a notoriously wobbly cockney twang when he played Bert in the iconic film, which has been treasured for decades.
As he collected a BAFTA prize – the Britannia Award For Excellence In Television – he took the opportunity to poke fun at himself.
“I appreciate this opportunity to apologise to the members of BAFTA for inflicting on them the most atrocious cockney accent in the history of cinema,” he said, according to the Mirror.
It’s not the first time he’s admitted his accent was far from perfect.
In December, he said: “Someone should have told me I needed to work on my Cockney accent.
“Nearly everyone in the Mary Poppins cast was a Brit but no one said anything.
“Years later I asked Julie Andrews ‘Why didn’t you tell me?’ – she said it was because I was working so hard.”
Van Dyke is set to appear in the upcoming Mary Poppins Returns, but not in the same role.
Instead, the 91-year-old will play Mr Dawes, Jr; a cameo part.
Emily Blunt – now playing Poppins – beamed: “He’s incredible; he’s got a zest for life that is infectious and he thrilled everyone.
“He gave us little snippets of the original between takes; he’s a magical guy.”
Mary Poppins Returns is out at Christmas in 2018.