The British Foreign Office was this weekend supplying the Department of Foreign Affairs with the names of the six people. They will be contacted straight away "as a precaution".

Litvinenko is believed to have been poisoned in the Pine Bar of the fashionable Mayfair Hotel. He fell ill later that day and died three weeks later. All seven employees of the bar have tested positive for radiation contamination.

A spokesman for the department said that "from this weekend, we hope to be in a position to have the names of six Irish people who were staying at the London hotel about the same time as Litvinenko. We will be getting in contact with them and advising them as a precaution to see their doctor and contact the Health and Safety Executive. Minister Dermot Ahern is being kept briefed on the situation. He has asked that every assistance be given to the individuals concerned."

The British authorities are chasing up anybody who could have been in contact with, or in the same location as, Litvinenko due of fears of inadvertent contamination.

However, Department of Foreign Affairs sources have stressed that it does not want to alarm anybody and that the Irish citizens were being contacted purely "as a precaution".

The UK's Health Protection Agency said there was no health risk in the short term for the seven staff of the hotel's Pine Bar and "in the long term, the risk is judged to be very small". The risk to hotel guests is judged to be "very low indeed".