Businessman Denis O'Brien has sold the remainder of his stake in Aer Lingus.

Shares in the carrier jumped by almost 5 per cent yesterday, the single biggest day of market activity at the carrier in five years.

Throughout the day’s trading, analyst speculation unanimously pointed toward Mr O’Brien unloading the last of his holding in the company, although this remains officially unconfirmed.

The businessman reduced his holding in the airline to under the 3 per cent level last month, through the sale of €4.7 million worth of stock, meaning he was not duty bound to report any further sale to the market yesterday.

Four blocks of shares, totalling more than 21 million units, were traded between 11.04am and 11.08am at about €1.32, although that volume greatly outnumbered the 12.75 million shares still held by Mr O’Brien before the beginning of the day’s trading. The sale of the total remaining 2.4 per cent of stock would have amounted to €16.8 million.

As regards a buyer for the stock, most analysts pointed to an international investment fund, with this suggesting fellow airlines Ryanair or Etihad were not involved, although this was not confirmed.

Certainly the overwhelming view was that Mr O’Brien had finished the job he began a few weeks ago.

“Given the volumes that have gone through and given the fact that he had already reduced his holding, it’s being put down as that,” said one analyst following yesterday’s activity.

“Certainly the expectation in the market is that he is selling down his stake.”

Another said: “There was a big block of stock around and not many people who own that kind of size.”

There was no official confirmation of Mr O’Brien’s move to end his relationship with the airline. The shape of the sell-off in four blocks led others to speculate there were at least three buyers in the market, with most pointing to international institutional investors.

However, regardless of who bought, as one analyst said: “It’s the largest dealing in the shares in over five years.”

According to a notice formally issued to the market earlier this month, Mr O’Brien reduced his holding to 12.75 million shares from 16.81 million on July 31st.

The stock’s closing price was €1.33 on the day, valuing those shares sold by Mr O’Brien at €4.7 million. That move reduced his holding to 2.4 per cent, less than the 3 per cent stake that obliges investors to inform the market of any transaction and therefore clouding yesterday’s activity in a degree of mystery.