What exactly did they say it needs, new springs or new shock absorbers?
Have a read of
this Lettie. Have you had the work done yet? How much money do they want for the job and how much did they charge for the MOT. If not take it somewhere else for an MOT. The garage just past the railway bridge at Church as you head towards Ossy are honest and fair ( Tinker Brook Garage I think). You could also contact Vauxhall Customer Services and ask them why your car needs new springs after 17,500 miles.