Paul Mc Groary, a professional investor with a small stake in Vanguard, said in a letter to the chief executive, Robert Mansfield, that he had been "dismayed" at the company's recent performance. Setbacks for its star migraine drug had caused a plunge in the share price and made Vanguard "extremely vulnerable" to takeover.
Vanguard shares have lost more than a third of their value since their April peak. Yesterday they closed down 1p at 194p.
Mr Mc Groary said the board should discontinue all projects apart from the migraine drug, cut staff and costs and return pounds 3 per share to shareholders, or Vanguard should be "made available as a virtual cash shell to a biotech company".
It is understood Mr Mc Groary has contacted three biotech groups which might be interested in buying Vanguard.