Where abouts in the Uk are you? Take it to a good indi. We might be able to reccomend one.
The dealer is right about the sensors causing the squeak but he is not right about it being normal. They squeak when the pads are worn as foxy has stated.
I had this exact problem. Change the pads and sensors (fixed it for me) and then if it continues to squeak think about changing the discs although this should not be necessary depending on the mileage the current ones have done.