FR have a smaller share in UK because they have a number of major competitors here: EZY, BA, FlyBe, Jet2, Monarch, Virgin & BMI until recently.
Yes but they have around 40 based at STN and most other bases are 4-6 aircraft. A rought guess would be 70-75 aircraft based in UK which is probaly more than Jet 2, Flybe, Monarch but far behind EZY.