I wouldn't have an MOT at a dealer. What Cranberry and Hora said:
MOT – go to your local council tester.
Service – ring around and get them to price beat (not match) as they're desperate for your business (I used to save about 50-75 on the 'going' rate). Also go to Halfords or National for 4L of approved oil and get them to put that in and save another 40 quid off the cost of a service.
Tyres – Get some prices from etyres or Black Circles. If you know you need tyres at the MOT/Service then you can tell them what you are prepared to pay. Any other time just get your tyres changed via etyres/Black Circles and have it done at home, work or at a garage local to where you are.