Spinningtop
Up until the end of 1994 you could do exactly what you suggest. Get the books, self study, buy some simulator time. Then when you were ready enrol for the exams (4 or 5 times a year I believe) and if you passed throw yourself at the job market with your newly gained licence and ratings.
But not anymore. Since the introduction of 'RGAT' in 94/95 the only way to achieve the qualifications is by attending a recognised course - they're not cheap and a huge gamble. Success is not guaranteed. There are 3 - Aerodrome, Approach and Approach Radar. Prices are approx £15K, £11K and £15K respectively.
If you're hoping to become an ATCO via the non-NATS ATSA route then your real hope has to be that the airport recruits and produces ATCO's from within. If they pay for your qualifications then sure, you'll be bonded for the cost of the courses for a period of time, but that works both ways - you have the job that you want, possibly where you want.
Bear in mind though that Airports are run by the beancounters too. The most sought after places will always be able to recruit already qualified controllers from other units which pleases the accountants - it means no risking money on people who may fail the course (and that does happen - regularly).
Good luck with your ambition.