London: Australia's outgoing High Commissioner Alexander Downer says Brexit will damage the EU, which is in denial over its mishandling of immigration.

Speaking to Fairfax Media from Australia House in his last few hours in the job, a candid Downer singled out the European institutions for criticism and said they needed to shoulder much of the blame for the Brexit result.

Describing the EU's handling of immigration as "chaotic" and its management of the eurozone during the Cypriot financial crisis as causing "catastrophic harm" he said it was Europe and not Britain that had the most to lose from Brexit.

Outgoing High Commissioner to London Alexander Downer Credit:AAP

"The European Union institutions don't admit it but I think it's clear that [Brexit's] going to substantially weaken Europe," Downer said.