Help with lpg please!!

I have a disco 2.0 mpi on a 1995 reg with gas conversion but recently my mpg has fell drastically although the lpg system has been serviced and tuned and when plugged in it saying it all perfect.
E.G...£22.00 got me to lakes and back and still some I managed 220 miles last year on the 22 quid.
Now I put 20 quid in other day and got 80 miles
HELP!!!!!!

price of lpg gone up..........

idea. rubber pipes shrink with the cold(mine did on a jeep) so nip up all pipe clips to eliminate leaks.

will try pies m8 thanks and also lpg gone up only 3pence here i get 59.9 pence a litre