The Australian chef, who was crowned the winner of the popular BBC TV series nearly a year ago, told BigHospitality he was currently working to secure planning and licensing permission for an empty site on Lower Regent Street before beginning a fit-out of the venue ahead of a spring 2013 opening.
Mair has acquired the building in a joint investment between himself, his private backers and the Spanish restaurant group which currently operates five sites including two in Barcelona.
"They approached me in January or February and I didn't know anything about their restaurants," Mair told BigHospitality. "I flew out to Barcelona and had a few meetings with them; it seemed like an interesting project.
"I have been going over to their restaurants doing a bit but my involvement is more about getting one opened here," he added.
Mair has now been working on the project for around six months and explained unforeseen delays had pushed back a planned opening from the end of this year to possibly March next year.
The focus is now on planning menus, testing dishes and recruiting and training staff.
"It is going to be a similar concept (to in Spain). We are going to have two floors - a pintxos tapas restaurant upstairs and more formal dining downstairs. It will be more Basque/Catalan than Spanish. I have got freedom with the food - but we want to try and keep it within the boundaries of the brand."
The main changes in the 140-cover London restaurant from its Spanish counterparts will be small modifications for British tastes and the introduction of English produce alongside more authentic products.
Speaking exclusively to BigHospitality after his Masterchef: The Professionals victory, the chef had declared his commitment to relaxed, mid-price point cookery; a commitment he said would be kept with the opening of Bilbao Berria London.
"The pintxos thing is interesting because nobody is really doing it in the Basque style - where you walk in and there is lots of food laid out ready to be eaten," Mair explained.
"We want to try and keep the prices down as well. Our concept is different to a lot of the other Spanish places that are opening up around London - we will have a coal-fired oven which is really great for cooking with because it gives the food great flavours."
Despite wanting to do some stages in Spanish restaurants, Mair explained he had not had time in the 'pretty quick year' since winning the BBC TV show which made his name. Instead he has paid numerous visits to Spain and completed work on his first book which will be released at the end of the month.
So when Mair has an odd moment off, which restaurants does he like to visit? "I have been to Barrafina quite a bit and that is always pretty solid; I have heard a lot about other places as well but I generally don't eat Spanish food in London because I eat so much of it when I am in Spain! I probably will do a lot more over the rest of the year - looking at what other people are doing," he concluded.