how do i disconnect the alarm immobiliser on my p reg vauxhall frontera?

my car went into the garage for a new clutch to be fitted and ever since ive had it back once the car is locked,as soon as you ope it with the key the alarm goes nuts and wont turn off,ive heard its a common problem on these and im sick i dont want it fixed i want it disconnected,im just gona do without but i dont know how to disconnect it can anyone help?