A small cannon sits on the window sill in David Brennan's London office, as if ready to defend him from any angry investors seeking better returns from AstraZeneca, the Anglo- Swedish pharmaceutical group that he runs.

But in recent weeks, the unusually favourable market conditions for his company mean he has had no need to contemplate loading the weapon, a gift from bankers involved in AZ's takeover of CAT, the UK biotech group, in 2006.