University
My advise would be to go to Uni and enjoy Uni life. I did a degree and a Masters degree in Biological Science.
At Uni you learn independance and life skills that flying school cannot teach you. As you will have appreciated getting a job is hard once qualified and if you have a background that is just GCSE/A-level then getting a well-paid job is hard, esp with what will be between £40-70K debt.
After Uni I trained as a Chartered Accountant, and through this have a fall-back incase once I have finished training no jobs are available.
GIve yourself the best chance of a job by once you apply to the airlines, your CV stands out a mile from the hundreds of ordinary ones.
Although a Uni degree etc is not a pre-requisite for airline entry you need to be able to stand yourself out and with this have the inter-personal skills that Uni and a job can give you.
Choose a degree that will open up a multitude of options once you have graduated and choose a job for 3-4 years that will give you a fall-back option, say optometry, dentistry, finance, law etc that are all recognised as good professions, then sacrifice holidays etc and save up and put the money towards to flying, therefore putting a strong argument to your Dad.
I was in a very similar boat to you and at 27 am part-way through my training doing modular, with PPL done and ATPL's underway, £15k saved up to pay for my training, therefore leaving a loan of £10k left to repay. I have 3 degrees and a Chartered Accountancy qualification to fall-back on.
Hope this helps.
Craig