There are sound historic reasons why a TD should not be arrested when travelling to and from Leinster House.

The rule was forged when the heat of the civil war was still searing and was designed to prevent one political party using the apparatus of the State to deny or thwart the ability of its political opponents to cast a vote in Dáil Éireann.

On the same premise, there are also very valid reasons why a member of the Oireachtas should not have their phone call records monitored or itemised. As Teachta Dála - messengers of the people - they will always expect to receive or make phone calls of a highly or sensitive nature - with a whistle-blower, for example, or with another source.

The rules are there and should be retained.

While the facts of this case have yet to established, difficulties might arise if those rules were to be abused by parliamentarians.

We have instances in the past (the distant past now) of TDs being arrested on suspicion of drunk driving but citing the Constitutional safeguard that they were on their way to the Dáil.

A similar argument was invoked by the MEP Luke ‘Ming’ Flanagan when he abused his position to get two penalty points cancelled.

In 2011 hundreds of calls were made from the Dáil casting telephone votes for one of the contestants in the RTÉ show Celebrities Go Wild.

Given that Michael Healy-Rae was a contestant, the provenance of the calls was immediately obvious. Healy-Rae’s late father Jackie was still a TD at that stage and paid back €2,500 to the Oireachtas once the situation came to light.

All telephone calls made by TDs and Senators are entitled by law to make free phone calls. They also benefit from free postage - the Oireachtas envelopes cause a media and public stir from time to time.

The RTÉ Investigations Unit submitted a request for information on phone call usage to the Oireachtas under the Freedom of Information Act. No information was given on the identity of those making the calls but it emerged that one TD or Senator had made some €2,000 worth of phone calls to a single Kenyan number over the space of three years.

An appeal to the Information Commissioner to identify the TD or Senator was turned down. For its part the Oireachtas said it did not log calls made by Oireachtas members “for reasons of privacy and confidentiality”.

This is in contrast to phone usage by civil servants and others in Leinster House, which are logged.

So it would have rested were it not for some excellent sleuthing from the Sunday Times which compared the dates of the calls with the attendance records and found that the person responsible was the Mayo TD Michele Mulherin.

Ms Mulherin confirmed to the Today programme on RTÉ Radio One today that she had made calls to Danson Kole, a friend who had previously been a political supporters and campaigner for her.

She insisted the calls were not personal but related to her work and specifically referred to a response to claims made by a media outlet about Mr Kole.

She was not able to confirm the number of calls she made, whether or not they were to the same number, and the costs involved. She did say she asked the Ceann Comhairle Seán Barrett to look into the matter and said she was willing to make a refund if required.

No matter, the costs were very high. It may be a marginal call as to whether the calls were professional or related to a personal matter.

While the monitoring of phone calls would have a chilling effect on the ability of any TD or Senator to do important public or parliamentary without fear of compromise, it is equally important that the facility of free phone calls is not abused.

However, in general it is very difficult if not impossible to devise a system that will prevent abuse while guaranteeing TDs and Senators independence from interference in their communications.