A British Airways Airbus A320-200, registration G-MEDK performing flight BA-2562 from London Gatwick,EN (UK) to Dalaman (Turkey), was enroute at FL350 about 140nm west of Frankfurt/Main (Germany) when the crew decided to divert to Frankfurt reporting smoke in the cockpit and cabin. A number of passengers and cabin crew to feel unwell. The aircraft landed safely on Frankfurt's runway 07C about 35 minutes later. A number of passengers and crew needed medical assistance. Parents of a passenger reported their child had called them from an ambulance advising a lot of people had fainted, others were vomitting and others were suffering from heavy nose bleeding. People were taken to ambulances on stretchers. The odour reminded of a massive fuel leak. The airline confirmed an odour event, a number of passengers and crew were assessed at local medical facilities. A replacement A320-200 registration G-GATH was dispatched to Frankfurt, resumed the flight and reached Dalaman with a delay of about 7.5 hours.