When Minister for Justice Alan Shatter decided to disclose an obscure occurrence involving Independent TD Mick Wallace and a garda, he should have known it would give his political opponents carte blanche to trawl the files to dig up any historical embarrassment of his own.

The second thing he should have known was that the mocking and scathing tone he adopted towards the end of the debate might rebound with a vengeance.

Lo and behold, Mattie McGrath took most people by surprise yesterday during Leaders’ Questions in the Dáil when he asked if Shatter himself had had any incident with the gardaí in which discretion had been exercised.

Clearly acting on inside information, McGrath referred to a Garda checkpoint in February or March of 2011, when Shatter was on the cusp of becoming Minister for Justice.

He asked about Shatter’s behaviour (was it appropriate and cordial?). He also asked if he had invoked the privilege of travelling to and from the Dáil (under article 15 of the Constitution a TD cannot be arrested travelling to or from the Dáil) as a means of avoiding a breath test?

Minister's statement
As it transpired, the Minister's statement last night showed McGrath got the date wrong, as the event had happened two years earlier. But besides that, many of the questions chimed with the response. Shatter said he had failed to complete the breathalyser test because of his asthma.

He explained that to the garda and also said he was on his way home from Dáil Éireann. After consultation with another garda, he was waved on.

The political repercussions of this are obvious. They are not position-threatening but will be a severe embarrassment to Shatter and will make his decision to disclose Wallace’s encounter seem foolish.

He mocked Wallace for not being able to remember his incident, using the phrase made infamous by Brian Lenihan senior in 1990: "mature recollection".

Shatter made no reference to the incident in the Dáil on Monday. He said his only such encounter with gardaí was when a guard wrongly warned him for driving in a bus lane last year.

Mature recollection
Now, on mature recollection, there is indeed such an incident in which a garda afforded him far more discretion than was given to Wallace.

There is no doubt that the matter will not rest here. Shatter will be pressed to give full details of the incident, his handling of it, and if, as McGrath said in the question he asked under Dáil privilege, “his behaviour and reaction to this request was appropriate and indeed cordial”.

And did he invoke Dáil privilege, as McGrath suggested, to bring the incident to an end? Shatter was also dismissive of Luke Ming Flanagan invoking the privilege of article 15. In Shatter's case it was clearly within his rights but that too has the potential for embarrassment.