Aer Rianta is very close to becoming part-owner of Dusseldorf airport, a spokesman said yesterday, but the deal is not likely to be completed until the end of the month. The move would see the Irish company take its first stake in a continental airport; it already owns 40 per cent of Birmingham airport.

The German authorities, who are selling a 50 per cent share in the airport for a figure thought to be around £150 million, said last month that it favoured a rival bid from the German group Harpen and an American partner. But it emerged this week that the Aer Rianta consortium - made up of the Irish company and its German partner, Hochtief - is now likely to be permitted to purchase the stake.

Aer Rianta is the minority partner in the consortium, but would not say yesterday exactly what stake it would own, or how much it expected to pay.

Some reports have said the Irish firm would put up around 10 per cent in cash, adding more of its equity in management skills and labour.

Dusseldorf airport has an annual passenger throughput of 15 million, compared with just 5.4 in Birmingham.

Aer Rianta, faced with the loss of its lucrative duty free business within the European Union, has been trying to build its international operations.