You need to register with the GTTR and apply for a place at a training college you want to go to.
First thing I would do is get in touch with a local school about doing an SAS (student associate scheme). You get paid £40 per day for 20 days (4 weeks) and get to experience what it is like to be a teacher. You don't do any teaching for obvious reasons, but you get to observe teachers, and help out as a TA during lessons.
You do need an undergraduate degree in the area you want to teach, but when you qualify as a teacher, after your training year, you also have a probationary year called an NQT (newly qualified teacher) year, after which you are qualified to teach.
There are three routes that I am aware of, B.Ed - Batchelor of Education which is a 4 year programme, PGCE - Post Grad Certificate in Education, for those who already hold a degree and finally, GTP - Graduate Training Programme, for those who hold a degree, but prefer a less formal, in school training approach.
I have done the PGCE, which is recognised internationally, so hopefully I can teach abroad in the near future.
Cheers for the sympathy lads