Why does it still work?

Heres a strange one.
Er indoors has a nice old discovery 2 with the lovely Td5 lump in it. As always, there are problems now & again but i have not come accross this before!.
For about 3 years the fuel pump has been squealing on start & pretty vocal in use. Over the last month or so, it has been really grumblng... Car still runs ok so maybe one day i will get one.. Am sure we have all had a round tuit moment or two.
Got the call today, " damned thing wont go past 40...." Off i go on a rescue mission. Gets to her & the engine is running & doesnt sound to bad. Hmmm.... best have a go. JESUS! would hardly climb over a cats eye!. Had a steady ride home & once there as its nice & quiet, thought i would have a listen. Turned off then turned key on but didnt start it. Odd.. no fuel pump sound.. Starts up ok but no oumph.
Guess the pump is scrap by now but why does it still work as i cant hear the pump working?.
Anyone got any ideas?....

Is the injector pump strong enough to suck Some up itself but not enough to run properly?

Edit: this is just a guess!

Would be my guess as well, similar thing with the tdi when the lift pump packs up

It's a Land Rover- they have a way of not working when there's nothing wrong and keeping working when they really shouldn't

It happens, it's like a kinda sealed boyle's self flowing flask... the pressure in the system will fail a bit day by day and in the end it will not run anymore .... or if you release the pressure somehow(e.g. remove the filter or the FT sensor to insert a gauge) then it will not start again

You also get low power when the pump is on the way out or the fuel level is very low. If you look at the injectors, the hole where the fuel goes in is very small, so you need a good fuel supply at high pressure to give them a full charge in the fraction of a second between injections. Yes, my TD5 will run for a bit if you disconnect the pump. Slowly, but it'll run.

The TD5 doesn't have a separate injector pump - just the fuel pump in the tank and the injectors themselves, which are driven from the camshaft.