How can PR teams respond to bomb threats?

The Tesco PR team have got a curveball to deal with at the moment.

Someone has been calling in bomb threats to Tescos stores.

Naturally, Tesco evacuated all stores and alerted the police. Presently it is thought that these calls did not originate from extremist groups, but more likely disgruntled stakeholders.

So how do you work that story? How do you convince your customers that your stores are safe, and explain why someone is so upset with Tescos they would go as far as phoning in bomb threats that cost the company millions of pounds.

Perhaps, speculatively, how would you handle the issue if it had been from an extremist groups, if terrorists did begin targeting the UK's largest employer. How could you possibly convince the public that your cheap prices are worth customers risking their lives?