how do you turn off the immobiliser in a ford galaxy ghia 2 liter petrol?

Hi I am trading my galaxy in this week, but i went to the garage to get fuel and tried to start it up but nothing happened, but that was ok can fix that just wait and it will kick in. But no the bl**dy immobilizer started i dont have a fob never had one with the car so i git out locked the door waited for five and tried again still sceaming so can you tel me how to get it off without me going to the garage as if i have to spend anymore money on this car before the middle of the week when i trade her in i will scream thanks jean