Vauxhall Astra 1600 SXI 2003?

My car has developed 'hiccups'. It only occurs after a long spell of touring/motorway driving in 5th gear when I slow down for e.g. build up of traffic. It starts to hiccup when I decelorate and again when I try to accelorate. If I disengage the engine by pressing the clutch the engine dies and I have to jump start it while I am decelorating. If I ignore the hiccups and manage to obtain a smooth operation usually around 50mph and keep it steady for 10 mins or so the problem disappears till the next time. What could be the cause/causes for this?