First off, you won't be fighting for a government, but for Her Majesty the Queen. You take your oath to her.
It would be wise to take advice as has been suggested, and I don't think you need to be quite so worried about UK recruiters - they are not targetted in the same way as I understand US recruiters are. Find one who is a colour sergeant if possible - these are genetically incapable of lying.
If you wish to take a commission, you will be required to go through a Regular Commission Board (these have probably changed since my day, when one's father delivered a cellar of recently looted Napoleonic cognac to the colonel and one picked up one's spurs and pips at the club) which will assess your fitness and ability for command. If you are a graduate, you will have some advantages (indeed, I'm not sure if nowadays non-graduates
can apply).
Once you pass out of Sandhurst, you will be a second-lieutenant of Infantry. (You should give some serious thought to which regiment you wish to join as this will inform your entire journey - it will be your family and your home, for the rest of your life - assuming sundry Prime Ministers don't amalgamate it into oblivion). A 2Lt is the lowest form of life, far less important than something you might wipe off your boot. Since you intend to join the infantry (not the Guards, one assumes) this will matter much less to you, but for any of the cavalry or elite regiments, you need to learn to carry heavy objects at speed, enjoy observation duty on winter's nights, and carry a tin of vaseline with you at all times.
Eventually, some fool will promote you by accident and you will become a real officer. This means you can drink tea all day whilst your sergeant makes you look good. Never fall for the illusion that you are in command. You are there to take the bawling when things go wrong, and to be a body upon which to pin medals when things go right.
I can't really comment on life as an infantryman, as I tried not to converse with them since they were usually wet and muddy.
To be serious for a moment, the Army is a wonderful life for a young man and you will find yourself. You will also make very good friends. However, you should understand that HM Army is significantly over-stretched at the moment, and you will (even in the Pay Corps) see action. You will find yourself tested. It's a long time since the Regular Army meant a few desultory engagements with the mango-wielding pygmies of Umboto Gorge between chandelier-lit dinners. This means that leave is foreshortened much of the time, and the dickless wonders of the MoD Penny-Pinching Corps will determine if you live or die. The military covenant has been severely curtailed since my day, and you may find real difficulty getting medical or psychological help if you are invalided out.
Therefore, make very sure that your reasons are sound for joining. And if you do, may I wish you the very best of British, and have a fantastic, exhilarating, challenging and deeply satisfying time. (And don't touch the Marines, you don't know where they've been).
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