Phone Leeds and ask if they can give you feedback on your application. Dont be rude or aggressive. They may only say that you 'didnt meet their requirements' which is usually code for 'we didnt like your PS or your reference', but you can ask if there was anything specific - like a missing GCSE grade for example.
You can't appeal the decision unless its based on something factual - they have misread your existing qualifications as an example - otherwise, you just have to take it on the chin and move on.