A former senior adviser to the Bank of England has highlighted unusual trading patterns in AstraZeneca before it publicly disclosed a takeover approach from Pfizer.

AstraZeneca revealed on Monday that Ian Read, chairman and chief executive of Pfizer, had first contacted it on 25 November 2013 to ‘discuss a combination’.

AstraZeneca subsequently staged ‘an exploratory meeting’ with Pfizer on 5 January 2014 in New York. Neither event was announced to markets.

In the six months until November 2013, AstraZeneca’s share price had lagged the wider FTSE 100, losing 1.5% while the index gained 4.7%.

Since November, AstraZeneca’s stock has surged 14.3% while the FTSE 100 has dropped 1.6%.

The divergence between the two was most marked in January when AstraZeneca rose by 8% and the index fell by 3.5%.

January also brought a spike in the trading of AstraZeneca shares. Between May 2013 and December 2013, trading volumes were consistently around £1.5 billion per month. This leapt to £2.5 billion in January, and has remained above £2 billion since then.

Since 31 October 2013, AstraZeneca has released three sets of financial results. Each of these featured double-digit percentage declines in both the company’s profits and earnings per share.

In a blog today entitled ‘AstraZeneca: Insider Trading Bonanza???’ for the Cass Business School, where he is a lecturer, Peter Hahn supposed that regulators would take a keen interest in these patterns, although there is not concrete evidence of insider dealing.

‘The lack of an AstraZeneca board announcement will certainly be questioned, but it looks like a dead certainty that many a regulator and lawyer will be very busy,’ commented Hahn, who from 2009 until March 2014 was a senior adviser to the Bank of England focused on the Prudential Regulation Authority.

A spokesperson for AstraZeneca declined to comment.