When voters head to the polls to elect Denmark's 13 MEPs in May next year they may also be asked to delete two Danish EU treaty opt-outs and to approve the kingdom's participation in the European patent court in a referendum.

The leader of the Liberal party and former Danish prime minister, Lars Lokke Rasmussen, will propose in a speech on Monday (12 August) in Norway that the Danes should remove opt-outs on EU defence and justice co-operation that were introduced almost 20 years ago.

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A third reservation on joining the euro is not to be touched, however.

"Time has come when we must do away with these reservations. The negative effects of, in particular, the justice op-out is so urgent that it would be irresponsible to continue to push it ahead. The prerequisite is that you have broad support at Christiansborg [the Danish parliament], and this is exactly what I am now offering," Rasmussen said in an interview with Danish daily Politiken over the weekend.

The plans to set up a European Public Prosecutor (EPPO) as part of efforts to clamp down on fraud committed against the EU budget shows how the Danish justice could pose problems.

The present government had earlier planned to hold a referendum on abolishing the defence and justice opt-outs.

But Prime Minister Thorning-Schmidt backed off on the commitment in June 2012 citing the general "anxiety and uncertainty" surrounding the European project at the time.

Denmark obtained four opt-outs from the Maastricht Treaty in 1992.

The opt-outs are outlined in the so-called Edinburgh Agreement and concern Economic and Monetary Union (EMU), Common Security and Defence Policy (CSDP), Justice and Home Affairs (JHA) and citizenship of the European Union.

With the opt-outs in the bag, the Danish people accepted the treaty in a second referendum held in 1993.

Signing up to the European patent court is a separate issue and would also imply a loss of national sovereignty, Denmark’s justice ministry concluded earlier this year.

The country needs a five-sixths parliamentary majority to approve the court or approval by referendum in order to join.

But despite a large backing in the parliament to remove some of the EU opt-outs, people may vote differently.

A survey by the Danish Greens Analyseinstitut earlier this year showed there is still a large majority (62%) against the euro and that a just 39 percent wants Denmark to join EU justice policies.

The defence opt-out is the exception, with 55 percent happy to scrap the measure.

With the EU summit in December designed to boost defence co-operation, Denmark's position on EU defence is likely to climb the political agenda.

Meanwhile, the idea of linking a referendum to May's European Parliament elections is a high risk game for the government, as it is likely to mobilise voters from eurosceptic movements.

For his part, Nick Haekkerup, Denmark's new EU affairs minister, declined to give the government's support for tabling the referendum next spring.