In and around Peterborough there are lots of good shops, with honest mechanics and service managers. I worked in the trade for 10 years, and continue to deal with many of the shops in the region as a part of my employment.
As others have said, your best bet for savings and peace of mind, is to do it yourself. Buy a floor jack, learn your safe lift points underneath your vehicle, apply parking break / block your wheels, and crawl under there.
As far as this "void your warranty" nonsense goes, it's a very common misconception. The Stealerships, as I like to call them, lead you to believe this, and want you coming back for the life of the vehicle so that they can continue to ream you. So long as any licensed technician or licensed oil change specialist performs the service, you will not void any warranty.
I do everything I can on my car because I hate anyone else touching it. I've seen some serious butchery and manglers in my time working in shops. Breaking bolts, neglecting to put in bolts, hiding damage, super glues, epoxies, JB weld, it is all very common. Bolts rust, plastic gets brittle and breaks.