i think at 25 i would go for the ATPL straight away. only because if you spend 3 years getting a degree at leeds anyway, all you will end up with is a PPL and a BSc and be 28. if you spent those 3 years flying you could easily be at CPL/IR level and looking for a job.
I don't know much about London Guildhall university, but i still think you start flying asap.