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Co-administrator of the challenge from the northern Welsh town of Harlech, Gwyn Headley, said he was jubilant and relieved after a nearly 10-month campaign to have Ffordd Pen Llech recognised.
While he felt slightly bad for taking the title of Dunedin and New Zealand, the gradients did not lie, he said.
''I feel sorry for Baldwin St and the New Zealanders, but steeper is steeper.''
There were 10 specific requirements which the Guinness World Records requires the world's steepest street to meet, but the Welsh challenge was given a dispensation for one of them.
As it is more than 1000 years old, Ffordd Pen Llech did not have any blueprints before the 1800s so did not need to supply blueprints as part of the bid.
Dunedin could still claim to be home to the world's steepest straight street as Ffordd Pen Llech twists and turns as it leads up Harlech Castle, a Unesco world heritage site.