The pharmaceutical company Pfizer has added its voice to the industry's concern about animal rights extremism.

Gill Samuels, executive director of science policy for Pfizer Europe, said the climate of extremist activity would restrict the company's ability to attract investment to the UK, despite the high quality of research carried out here.

The concern comes as the government prepares to announce powers to combat the violent behaviour of a minority of anti-vivisectionists.

Pfizer spends £10m a week on research and development in the UK alone, but is increasingly having to divert funds to pay for extra security.

This week the chief executive of GlaxoSmithKline, Jean-Pierre Garnier, said his employees were being "terrorised" by extremists, who were "despicable cowards".

Dr Samuels said: "We agree with Jean-Pierre Gar nier's comments that animal extremism presents a business risk for the pharmaceutical industry and could hinder the development of important new medicines if it is not addressed."

But she dismissed a suggestion Pfizer would withdraw scientists from the UK.

"The reality is that R&D investment decisions are long-term commitments, and are determined by many factors, not a single issue. "Pfizer, like all major R&D investors, will conduct its science where it is most welcome."

The home secretary, David Blunkett, will announce new measures today to tackle what he calls "internal terrorism".

He is expected to introduce a specific criminal offence of protesting outside someone's home in an intimidating way, and will make it an arrestable offence to return to someone's home after being found guilty of aggressive behaviour. Anti-stalking laws are also expected to be extended.