steve, from what I got, it is not your fuel pump but the filter module unscrewing itself. Check on this forum for a way of fixing it. The description is for a ZTT but should essentially be the same. Here are some more instructions "Petrol pump and the filter are both located in the tank. Pump is underneath RHS rear seat. Filter under the LHS rear seat. When ignition is switched on, you should hear pump hum for 2-3 seconds. If so, lack of fuel at engine will probably be why it won't start. As described by Tatts, this is due to filter case unscrewing and releasing pump pressure. It's a design fault caused by the pipework pushing on the casing. It's very common problem and can be fixed using the 'Orange Clip' gizmo (available from Rimmer Bros at some silly price or other. Sometimes on eBay. If it turns out to be this, here's some pics from my own repair job.
Remove rear seat cushion. Remove three screws and remove access panel on LHS floor. White plastic cap of filter is underneath. Petrol pipe to engine is attached to cap with green self-sealing clip. Press lugs together and pull pipe out.
The steel strip is a removal tool I made so you can use a spanner rather than a hammer and chisel. Pull the filter unit as far out of the tank as it will come without messing with the float and pipework underneath it. There's a thick rubber gasket around neck of tank, not visible here. The end cap is screwed onto the body bayonet fashion. The join is just above the steel band. The cap is sealed with a large thin O-ring that fits on a shoulder on the cap. Mine was distorted so I had to fit new. Only available as a filter element kit costing around £45. Here's the cap and O-ring (not in position here). Central spiggot has small O-ring to seal the cartridge. Bottom of case has similar spiggot. Sorry don't have picture of the orange clip, but it will only fit in one place. That's directly under the outlet pipe connection on the end cap. It goes across the join and stops the case unscrewing. Refit filter in tank, but first ensure rubber gasket is seated all around tank neck before lowering filter (important or it will leak). Replace metal sealing ring with correct torque of 28ft.lbs/35Nm." There is more of this on here The "clip to hold the filter housing together is available here. Hope this helps to get you going again until I get the service manual posted. Good Luck.
Okay, so now you can download the complete service manual for your MG right here. It is in electronic format and comes as an ISO. All you have to do is either mount it to your computer or burn it to CD. I double checked it for functionality and it does have all the information that you need. It is a 700mb file and will take awhile to download :-) good luck.