Former Bank of England Governor, Mervyn King, is seen appearing on the BBC's Andrew Marr Show in this photograph received via the BBC in London, Britain March 6, 2016. REUTERS/Jeff Overs/BBC/Handout via Reuters

(Reuters) - Britain should decide its own immigration policy and stop pretending Brexit is compatible with staying in the European Union’s single market, a former governor of the Bank of England said on Monday.

Mervyn King, who steered UK monetary policy for 10 years to 2013, told the BBC that supporters and detractors of the EU should start to look at Britain’s vote to leave it as an opportunity.

“There are opportunities to Brexit that we should take (...) and I think we should look at it in a more self-confident way than either side does at the moment,” he said.

“I don’t think it makes sense for us to pretend that we should remain in the single market, and I think there are real question marks about whether we should stay in the customs union,” he said, adding that Britain had to decide its own immigration policy.

Most mainstream economists support Britain’s continued membership of the single market and any signs it might lose access has tended to drive down the value of sterling.

Leading EU politicians have said that access to the single market, in which goods and services trade tariff-free, is only possible in exchange for allowing free movement of EU citizens.

“I think the referendum made it clear that people wanted control over immigration ... that is not negotiable and it would be a big mistake to put it into the basket of things that we have to negotiate with former partners in the EU,” King said.

British Prime Minister Theresa May has said she will start the process to leave the EU by March 30 but there has been scant detail of what form Britain’s trading relationships will take after that.