If you're a student then you don't have any income do you? If your girlfriend is only earning £13,000 a year and you are a student then how do you hope to be offered a mortgage or pay one? If you do get a job then are you sure you're going to be in continuous employment for the next 25 years to be able to pay that mortgage?
Secondly, you mention buying the house with your girlfriend. Are you still going to be girlfriend and boyfriend for the next 25 years while you are paying the mortgage off? If you are getting married soon that's different but the relationship's very loose and you'll both be tied for 25 years with a mortgage.
You don't seem to have any real plans made or understanding of the requirements and responsibilities of a mortgage. The world has changed in the last 25 years since my wife and I bought a house and paid the mortgage off in four years. Not only are you required to meet very strict criteria today but you have to establish a very strong base for the next 25 years from which to pay the mortgage. If you are in just a loose personal relationship and you have no job I don't think you'll have much success. Perhaps rent somewhere for a while until your life is more stable.
I hope you get things sorted. Good luck.