The Metropolitan Police joined the hunt for missing Madeleine after a request by Home Secretary Theresa May, with Prime Minister David Cameron's backing.
It has been revealed that detectives spent three days with police in Barcelona, between November 23 and 25, and have also travelled to Portugal three times to look for leads.
Scotland Yard say there will be no limit to its examination into Madeleine's disappearance from a holiday flat in Praia da Luz back in 2007, and there are now 30 people working on the case known as 'Operation Grange'.
A Scotland Yard spokesperson said there had been 'good co-operation' with Portuguese authorities:
"The review continues. There has been very good co-operation with Portuguese authorities and liaison will continue.
"We are not prepared to discuss specific details of these visits nor speculate about any future deployments to Portugal or elsewhere."
"It is a big relief to us that our Government finally agreed for a review to take place.
"We are grateful to them and to the Metropolitan Police Service for undertaking this fundamental and highly valuable procedure which has been underway now for several months.
"Although it will be a lengthy and difficult process, it is definitely a major step forward for Madeleine."