I was considering the same, when I was younger. Here is my summary. It's been a while, so it may me somewhat out-of-date.
> Sell your soul to Air Force for 5 years. Hope you get picked.
Nuf said.
> Work.
Getting a pilot license is expensive, and it is a life-style. But the good news is that 3-5 years you can be flying regional flights. And in 5+ years you can fly international.
It's all about accumulating hours.
The cheapest way is to get a job, any job, and pay your way till you get professional license. This will put you ~$30k in the hole, and won't allow you to fly passenger jets. But you'll be able to start doing actual paid work. Consider it an alternative to college degree.
Next step is to accumulate 250 hours by any means necessary, to get flight instructor license. Surprise surprise, unless you get a job flying, you'll need to rent a plane for this out of pocket.
Once you get instructor license, you can start working for a flight school, keep accumulating hours, and get paid for it.
Next step is to slowly pay your way through more and more advanced certifications (night flying, instruments flying, etc), concluded by airline pilot certification. For this you need about another $50k-$70k worth of training altogether, and 2.5k flown hours.
Congratulations, now you can fly jets. But nobody will hire you. At best you will be flying regional airlines, till you accumulate 5k-10k worth of hours. Major airlines won't even reply to you, before that.
Also, if you're in UK, flight certification is significantly more expensive. Make it ~140k GBP total.
tl;dr: $100k in the hole, and ~3 years later, you can be a junior airline pilot.
> Get lucky
Some Airlines offer 5 year contracts and direct entry program to get you to pilot within 2-3 years. But you're pretty much signing up for 5 years of working for substantially bellow-average salary, but with the prospect of your training being fully covered.