Sir David Chipperfield has accused politicians of lacking courage and vision at a time when "ideas and principles are under siege" and said architecture has become "contaminated by cynicism".

Speaking at the RIBA Royal Gold Medal dinner in London last night, Chipperfield praised the work of 2017 medal laureate Paulo Mendes da Rocha, saying the Brazilian architect has created "an architecture that emanates ideas and optimism".

"You arrive in our country as our government and our unelected prime minister are isolating us from Europe, as our country begins to become in my opinion pessimistic and un-optimistic, and little Britain becomes littler," said Chipperfield, addressing Mendes da Rocha, who attended the dinner held in his honour.

"In our transactional world, where ideas and principles are under siege and our politicians seem to have no courage or vision, how refreshing to be reminded that even an architect can be brave and idealistic," he continued.

Mendes da Rocha, 88, was awarded the RIBA Royal Gold Medal for his lifetime achievements at last night's dinner, held at RIBA headquarters in Portland Place.

Speaking to Dezeen in an exclusive interview earlier this week, the Brazilian architect discussed the lasting impact of Brazil's military dictatorship on his career, during which he was banned from teaching or practicing in his own right.

Chipperfield, one of the UK's leading architects, praised Mendes da Rocha for the vision displayed in his architecture, despite the persecution he suffered.

"In Paulo Mendes da Rocha we celebrate not only a highly talented architect, but an architecture that shows us how to deal with the big and the small, with the practical and the ideal," said Chipperfield, who is a past recipient of the Royal Gold Medal.

"He has shown us how, in a profession so contaminated by cynicism, professionalism and self promotion, how to be visionary and humane, courageous and humble. But above all to give us an architecture that emanates ideas and optimism."

Mendes da Rocha set up his São Paulo-based practice in 1955 and completed his first project – the Athletic Club of São Paulo – two years later.

Prolific in his native Brazil, the architect has designed just a handful of buildings overseas – the most recent of which the National Coach Museum in Lisbon.

Paulo Mendes da Rocha joins RIBA's eminent list of Royal Gold Medallists, which includes late British Iraqi architect Zaha Hadid and Portuguese architect Álvaro Siza.

This is the first time Chipperfield has publicly spoken out about his opposition Brexit since signing an open letter backing the Remain campaign for the UK's EU referendum.

Since Britain voted to leave the EU in June 2016, architects and designers have been vocal about the disastrous effect Brexit could have on the UK's creative sector – with hundreds lending their names to Dezeen's Brexit Design Manifesto.

The industry has also rallied to protest the election of Donald Trump to US president, with Steven Holl, Daniel Libeskind and Snøhetta condemning his recently imposed travel restrictions on seven African and Middle Eastern countries.

Chipperfield, 63, received a knighthood for his contribution to architecture in 2010 - the same year he was awarded the Royal Gold Medal - and curated the Venice Architecture Biennale in 2012. He is currently working on plans to convert the former US embassy in London into a luxury hotel and for the Nobel Center in Stockholm.

Chipperfield came in at number 10 on the inaugural Dezeen Hot List – a guide to the industry figures our readers most want to read about.