several possible causes, blocked fuel fillter, empty fuel tank, fuel pump problem, or and engine management problem (damaged sensor, or poor connection to ecu)
if its a sudden loss of power (eg the engine effectively cuts out) its likely to be a sensor problem possibley tps (throttle position sensor) this could cause the engine management to think the throttle is closed and there for no air is entering the engine, so it shuts off the fuel supply.
rovers are renowned for electrical glitches, so best be is to take it to a rover dealer and get them to plug your car in to a diagnostics tester. this will ask the engine computer if any sensors are not sending a signal to it, and then hopfully you will beable to find the fault and rectify it!!
Richard Warrington, February 2005