British journalist and author Simon Jenkins has said that Pfizer's decision to move its headquarters to Ireland, as part of its $160bn merger deal with Allergan, is a text book example of the kind of corporate tax avoidance which should be made "illegal."

He writes, "The decision of the American drugs giant, Pfizer, to merge with Dublin-based Allergan, thereby “relocating” its headquarters to Ireland is not because some wizard potion has been discovered in the hills of Connemara. It is to dodge tax."

Moving its headquarters to Ireland will result in a significant reduction in the total amount of corporation tax paid by the company - The Irish Times estimates that Ireland could gain an extra €620m per year after the completion of the deal.

However, the newspaper notes that while the company's revenue will be channelled through Ireland - it may ultimately pay tax locally in other regions with even lower rates.

US President Barrack Obama has called these so-called tax inversion deals "un-patriotic."

Candidate for the democratic nomination in the 2016 US presidential election, Hilary Clinton accused the company of using tax loopholes to avoid paying its "fair share."

In a statement she continued, "for too long, powerful corporations have exploited loopholes that allow them to hide earnings abroad to lower their taxes. Now Pfizer is trying to reduce its tax bill even further."

Republican front-runner Donald Trump said that the deal is "disgusting" - but he blames high taxes set by the US for these companies moving their business elsewhere.

Irish Agriculture Minister, Simon Coveney told Newstalk that "nobody is using Ireland as a tax haven" - he highlighted the other reasons why companies come to Ireland, including our skilled workforce, and native English.

The US Treasury Department has issued a letter on tax inversion deals, saying that it is reviewing means of stopping them taking place.

It plans to release a guidance on the matter later in this week.