The Government has started giving advice on terrorism to bigger businesses in London:
"More than 300 firms, including Tesco and HSBC, have been advised to consider counter-terrorism measures such as searching staff bags.
"The initiative, supported by MI5, also stresses the need for all businesses to put contingency plans in place."
Without wishing to spread panic, these are probably sensible precautions for the smaller concerns as well. More here.