The Irish Government’s annual legal costs will increase after Brexit because the UK will no longer influence negotiations on its behalf or help to transpose EU legislation into common law.

A source at the European Commission told The Times that the government’s legal bill could increase by “tens of millions” per year.

Lucinda Creighton, a former Irish minister for European affairs, told The Times that the government needs to start working on a strategy to deal with the issue.

She said: “As legislative changes are initiated in the commission, they usually call out for inputs from member states, civil society and industry. They also set up consultative working groups for stakeholders.

“We have limited capacity on all fronts and are often absent from these early consultations. As legislative proposals develop, we are forced to heavily rely on the UK to watch our back. This applies to the bureaucratic capacity of the UK — their mission in Brussels and their government departments — but also, crucially, their very well-resourced industry bodies. They have enormous resources to develop studies, monitor legislation and lobby for concrete amendments.”

Pointing to the financial services lobby in the City of London, Ms Creighton said: “We have no equivalent and so Ireland is heavily dependent on such UK entities to protect and advance the interests of the financial services sector as new EU regulations evolve.

“Those member states with similar legal systems and cultures inevitably have to co-operate to interpret and implement EU directives.

“In our case, being part of the common law system, Ireland inevitably co-operates and co-ordinates closely with the UK. When the UK leaves, we simply cannot fill that void that the UK’s absence will create. We have a tiny mission in Brussels and a relatively tiny government bureaucracy in Dublin.”