polo using lots of petrol. lambda sensor?????

[steve-the-polo]

i asked a while back now about my wifes polo using lots of petrol & got no replies back. she has a p reg 1996 1000cc cl polo thats using lots of petrol. been told it could be lambda sensor in the exhaust down pipe, told that if its gone faulty its very likely that the car will start to use more fuel, anybody out their that could confirm this for me before i spend money on this part. i do know that it only has has one on it and thats before the cat. dont know how many wires on it mind.....! help thanks people.