The Government’s attempt to secure special treatment for Irish citizens living in Britain should the UK choose to remain in the EU could be in jeopardy amid concerns in Brussels about the legality of the move.

The Irish Times understands the European Commission is concerned that attempts to exempt Irish citizens from in-work benefit restrictions could be in breach of EU law.

Among the concessions secured by Britain at a key EU summit in February was the right to restrict in-work benefits – tax credits paid to specific categories of workers – to migrants. This would mean non-British workers would be subject to certain restrictions over a four-year period.

Irish officials have been working behind the scenes to ensure Irish citizens are exempt.

It is understood officials are focusing on protocol 20 of the Lisbon Treaty, which deals with the common travel area and states the UK and Ireland “may continue to make arrangements between themselves relating to the movement of persons between their territories”.

But officials at the highest level of the commission are understood to have concerns about the legality of the move, arguing the relevant article concerns the common travel area between the two jurisdictions rather than a common labour market.

There are also concerns that other member states could oppose the measure on the grounds that their citizens are being unfairly penalised.

The issue threatens to come to the surface in June should Britain vote to remain in the European Union. In the event of a Remain vote on June 23rd, the European Commission will move to enact secondary legislation to give effect to the renegotiated British settlement secured by prime minister David Cameron in February.

This will include a legislative proposal on the restriction on in-work benefits, which will have to be approved by the European Council and MEPs in the European Parliament.

Taoiseach Enda Kenny raised the issue with Mr Cameron during a bilateral meeting in Brussels at the EU summit in February.