fuel pump problem????????????

hi guys went out this mornin 2 take the sproggs 2 school n my m plate v8 disco wouldnt start. its a v8 on lpg so i got me bro 2 give me a tow . still wouldnt start on petrol but did start on lpg as i was being towed. called out the aa and after a bit of head scratching he seemed 2 think the fuel pump was either nackered or a bit lazy .he tried bashing it with a bfh while i turned it over but still no joy. on this description does it sound like a nackered fuel pump 2 u guys? . he said the fuel pump is in the tank . how long would it take a decent mechanic 2 change 1? cheers 4 any help