Rover 25 Fuel Tank Problems

where is the fuel tank vent and how do i unblock/replace it my engine management light is on cos of it and it keeps juddering sometimes thanks

Does anyone know exactly where the Fuel Tank Vent is located and is it possible to see if it is partly blocked / Clogged. To start the Car I need to hold the Accelerator halfway down. When I pull in to a Station for Fuel there is a "gasp" ...