Did you get the new starter bonus? If so, it wouldn't surprise me that they have reduced your basic by the amount of the "bonus" you get!
The uk salary in STN should now be a basic of £74k. Not sure what base you are getting, but looks like they are doing the classic trick they always have done, of agreeing a "deal" for current contract staff, and anyone new that gets a Ryanair contract a few weeks after the "deal" was "agreed" gets a pay reduction...this is what they did with FO basic salary to drive the wage down to a low of 20k basic when it was well over 40k! (They are now shouting to high heaven about the pay rise FO's have got, when in reality it is still less than the wage 10yrs ago!)