If it's the K-series engine then you can probably get at the drain plug with a ratchet and socket just reaching under, without jacking it up. I seem to remember that I had to jack my Rover Metro up just an inch or two in order to slide a drain-tray under. I can't for the life of me remember if the drain plug needed an A/F socket or if it was metric! And nobody mentions what size it is on this forum...

forums.mg-rover.org/showthread.php?t=303498

Remember to buy a 5l pack of oil - not a 4 litre - because it takes about 4.5l. And have an empty 5 litre can and a big funnel to hand so that you pour the old oil into it and take it to your local re-cycling yard. We used to use Duckham's back then. Nice green stuff as I remember! The MG-Rover forum suggests Castrol Magnatec or Castrol Edge.