It offers a "back door" route for the state to take ownership of large chunks of Northern Ireland. But despite this, Sinn Féin is continuing to withhold its support for Nama.

In the Dáil last April, communications minister Eamon Ryan (below) said about 15% of the distressed loans Nama planned to buy were from Northern Ireland, meaning their value could be as high as €13bn.

A spokesman for the Department of Finance confirmed the lands or developments in Northern Ireland would be expected to transfer to Nama if the loans taken out on them go into default. This would mean that, however temporarily, the state would own these properties in the North. But a Sinn Féin spokesman said the party's belief that Nama is not the "best route to go down" was not affected by this.

"We come at it purely looking at the implications for the whole country, and as far as we can see Nama is a bad idea," he said. "As for the North, we've always advocated Irish reunification, but this is not the political reunification we would desire."

Establishing the exact amount of Northern Irish land involved has been problematic. Last month this newspaper reported that the amount of Northern Ireland-based 'bad' loans could be much lower than the 15% estimated by the minister.

The Department of Finance spokesman confirmed around €22bn of lending is in the UK. "Most of it is within the M25 – London and southeast England," he said.