I have no experience other than that I am currently applying as an ATCO to NATS, with my final selection assessment day pending. I am also a Royal Navy ATCO applicant.
How do I view the situation at present?
NATS are recruiting, they expect the aviation sector to grow, so accordingly the ATC sector will grow. If you are smart and have the aptitude, you already have the skills required to apply successfully.
Independent training
I haven't looked into this too much, as I done have the money lying around to be honest. But I believe it is still as expensive as ever. I haven't heard of many towers sponsoring people out of the blue. I think most of those situations are people who already work at the aerodrome and who they then offer the ATCO job. Other may correct me of course.
Military
Both the RAF and the RN use Air Traffic Controllers and Air Traffic Control Officers.
An Air Traffic Controller is an "other rank", i.e. does not carry a Queen's Commission. These are still skilled controllers, but their level of responsibility is not expected to be as great as their commissioned counterparts. Their pay is about 10k per annum less, but the job is easier to get into. If you do well early on, there is the option for your Commanding Officer to suggest you for becoming a Commissioned Officer and keeping all of the benefits which that brings.
An Air Traffic Control Officer is a bit closer to the civil aviation role (by my limited understanding). The responsibility level is expected to be higher, i.e. if traffic levels are expected to be higher, an Officer will be on sector.
What's the difference between RN/RAF/Private/Public?
Royal Navy: Fleet Air Arm. It includes the opportunity to work off capital ships such as HMS Ocean and to truly 'travel the world'.
Royal Air Force: Similar types of controlling to the RN largely, however you will always be land-based.
note: For both military applications, the FATS test will be a requirement. Rumour has it, this is easier than the FEAST of civil aviation. I may be able to let you know in a few months time, as I will have done both.
Private: Private airports often employ their own Air Traffic Control Officers. This is said to be a very rewarding job, and offers location security.
Public: NATS is the public ATC provider in the UK, and over parts of the North Atlantic. This large organisation is the only "free" way to train without signing up to a lengthy service contract. NATS uses all types of controllers (good and bad - no I kid..) from Approach and Aerodrome to Area controllers. These jobs I believe differ hugely from one another, and upon application you can never be sure which role you will be asked to fulfil. So if you want to be in a tower, be mindful that NATS may choose to shatter your dream.
NATS is a Public Private Partnership, and as such it needs to make money. The business needs of the company drive its recruitment and posting process. As such, the only way to know where you'll be living before applying, is to work for a private airport. NATS could post you to anywhere in the UK (or Gibraltar I think?). This includes Northern Ireland.
What do I think you should do?
Take a step back for a moment. I can see that you are enthusiastic, and that's great. But you need to be looking at the bigger picture.
Firstly, choose your further education wisely. It is almost always a mistake to study something you do not have an absolute passion for, just in case it helps win a job.
Then, choose your career path. If you are absolutely desperate to control, and are willing to be paid a modest wage for it, becoming a Non-Commissioned Controller might be for you! Compared to any of the other options, it is by far the easiest way to get in the hot seat.
If you want more remuneration for your work, then consider the other options after careful personal research.
No matter what you decide, good luck!
Phil