No. The insured is not covered under any section of the policy other than emergency medical expenses.
If they travel to a country or area which the Foreign & Commonwealth Development Office (FCDO) advises against visiting, GTG customer's are not covered for claims resulting from any terrorist activity. If they are not sure what the FCDO's current attitude to your destination is, please ring them on 020 7008 1500 or visit their website, www.fco.gov.uk
Apart from travel to these "non-recommended" countries, medical expenses and personal possessions are covered against terrorist attacks, but cancellation claims are not, unless you buy GTG's additional terrorism cover. If their destination has recently become more dangerous, their tour operator will usually agree to switching their booking elsewhere.