AstraZeneca (AZ), the FTSE-100 pharmaceuticals group, is preparing a search for the successor to the chairman who helped it fend off Pfizer's £69bn takeover bid five years ago.
Sky News has learnt that the drug-maker's board is at the early stages of planning to seek an eventual replacement for Leif Johansson, who has chaired AZ for seven years.
Sources close to the company said there was no formal timetable in place yet for Mr Johansson's departure, but indicated that AZ's nomination and governance committee was starting to consider the issue more formally.
Succession planning has taken on a greater focus for a number of the Anglo-Swedish group's leading shareholders because, unusually, Mr Johansson and chief executive Pascal Soriot took on their roles within four months of each other.
While a definitive decision about which of the pair will leave first has not yet been made, one investor said they expected the chairman to step down within the next 18 months, giving his successor free rein to identify Mr Soriot's replacement.
AZ and GSK, the two biggest players in Britain's pharmaceuticals industry, are both seeking new chairs, with Sir Philip Hampton having announced his decision to retire from the latter several months ago.
Under revised corporate governance rules, the chairs of FTSE-100 companies are no longer deemed independent if their cumulative boardroom tenure exceeds nine years.
The revamped code is having a significant effect on corporate Britain, triggering searches for chairs at companies including British American Tobacco, GVC Holdings and Vodafone.
Previously, the nine-year guideline did not apply to chairs.
Mr Johansson was paid a total of £690,000 by AZ last year, making him one of the best-paid chairs of a FTSE-100 company.
In its latest annual report, AZ said it had engaged in "continued routine succession planning for the roles of chairman, CEO and CFO, in each case with the assistance of the search firms MWM Consulting and Korn Ferry".
Mr Johansson played a key role in securing AZ's independence when it rebuffed a proposed £55-a-share takeover by Pfizer - a controversial approach which raised questions about the merits of allowing a major British scientific research powerhouse to be swallowed by a transatlantic rival.
While many shareholders were delighted at AZ retaining its independence, the company drew criticism for declining to link executive pay targets to the level at which the drug-maker said Pfizer had pitched an inadequate bid.
AZ has continued to stoke investors' anger by paying Mr Soriot £11.4m last year, despite huge revolts at its two previous annual meetings.
The company has signalled positive results from an ongoing push into earlier-stage cancer treatments, and has seen its shares rise by just under 10% during the last year.
An AZ spokesman declined to comment on Monday.