You generally need 6 months vaildity - check out the Turkish Consulate website for up to date information. http://www.turkishconsulate.org.uk/en/default.asp
Always check out the country you intend to visit on the Foreign Office Website http://www.fco.gov.uk/en/travel-and-living-abroad/ or that country's consulate website for up to date current information. Don't always rely on your travel agent as selling holidays is their business not necessarily giving visa/passport information.