Yes, it's possible. My son has just switched courses within the same university. He emailed admissions about it, and was asked to fill out a form, including a personal statement. The form had to be signed off by the heads of department from his old subject and from his new subject. They checked that he had sufficient UCAS points for the new course and that he had a good attendance record from his first year. It only took a morning to sort out. The university will send a Change of Circumstances form to Student Finance, so it shouldn't affect his loans/grants.