Bank of Ireland's 10 per cent rally on Friday is of cold comfort to Prem Watsa, the legendary value investor and head of Fairfax Financial in Toronto.

Shares in the bank, which have been battered in recent weeks amid concern over its exposure to Brexit, are down almost 29 per cent to 24 cents since Canada’s answer to Warren Buffett sold a chunk of the stock in March last year.

Watsa and US billionaire Wilbur Ross were among a group of audacious investors who snapped up a 35 per cent stake in the bank for €1.1 billion in 2011 when it faced the threat of joining the rest of banking system under state control.

Fast forward to 2014, and Fairfax and Ross cashed in a third of their chips at almost 33 cents each – more than three times their initial investment.

Chances are, however, that Watsa’s now ruing not joining his pal Ross when the New Yorker went on three months later to flog the remainder of his holding. He netted a total €500 million profit.

Even after selling more stock last year, Watsa retains a 2.4 per cent holding. With polls indicating that the British public could very likely vote to leave the European Union next week, Bank of Ireland is seen as one of the most exposed, with more than 40 per cent of its loan book in the UK.

Even if the UK does pull through, Irish banks are continue to struggle to grow their loan books as households and businesses continue to repay debt at a faster rate than those taking on new borrowings.

The heightened political pressure on lenders in recent months to cut variable mortgage rates hasn't helped investor sentiment – even if Bank of Ireland chief executive Richie Boucher is showing no signs of budging on that front.

Still, Watsa is probably not alone wallowing in regret.

Minister for Finance Michael Noonan is still holding an almost 14 per cent stake on our behalf.