sounds like an ignition amplifier fault. this used to be a ballisted resistor when cars had an ignition coil. however with modern electronic ignition i would suggest you take your car to an auto electrician to rectify the problem. parts can cost between �40 and �400
this is not necessarily a ignition problem but could be a fuel problem, there could be a lack of fuel pressure of which means the fuel pump could be on its way out, but it could also be a dodgy fuel pump relay as they are prone to go