European Central Bank president Mario Draghi said yesterday that negotiations with Britain on changes to its relationship with the European Union must preserve the “extraordinary achievements” of the euro and the EU’s single market.

Draghi was responding to questions by two senior European Parliament members who urged him to take a stance on efforts by British Prime Minister David Cameron to secure recognition that the EU is a union with more than one currency.

“The treaty is very clear on this. It says that the union’s single currency is the euro,” the ECB chief said, after saying he did not want to comment on a political question.

Cameron is seeking a new deal for Britain before putting continued EU membership to a referendum before the end of 2017. He sent a letter to European Council President Donald Tusk this week outlining his main demands, including guarantees that the eurozone would not discriminate against EU members that are not members of the single currency.

The treaty is very clear on this. It says that the union’s single currency is the euro

Britain and Denmark both have permanent opt-outs from joining the euro. Other countries that have joined the EU since the currency was created are obliged by their accession treaties to adopt the euro once they meet the criteria, although some – such as Poland – are reluctant to do so.

Lawmakers from both the centre-right European People’s Party, the largest political group in the EU legislature, and the Socialists, the second biggest faction, said Cameron’s letter seemed aimed at eroding the official status of the euro.

Pervenche Beres, a member of French President Francois Hollande’s Socialist party, said Cameron was trying to create two Europes – one with the euro and the other without it – and his call could obstruct what she called the more urgent priority of deepening eurozone integration.

Werner Langen, a member of Chancellor Angela Merkel’s conservative Christian Democratic Union, also urged Draghi to take a position on what he called Cameron’s attempt to undermine the single currency.

“We want to keep two objectives in the future,” Draghi replied. “One is the single currency and the second is the single market. Everything that will come out of this complicated interaction between the different souls of the union will have to preserve these two extraordinary achievements of the EU.”