I'm a PhD candidate at the Department of War Studies at KCL. If you want to drop me a private message, I'm happy to offer what advice I can, though I've got a couple of deadlines coming up, so I may not be able to do so immediately.

Some thoughts, which may be contradicted by people more knowledgable than I.

First off, I don't know who told you that a PhD is undesirable. My experience, though hardly conclusive, is that it isn't, though it may not be necessary. If you look through the ranks of people associated with the top think tanks and policy institutes, most of the top people have PhDs and those who don't are often either registered with a programme or have extensive work/life experience in the armed forces or government. There are, of course, other career paths, but many of them aren't going to be open to a British citizen without military or governmental accreditation. The other thing to note is that there are lots and lots and lots of MAs from very good universities out there in the job market. A PhD is hardly going to make you flavour of the month on its own, but it does put you one step up the rung academically and if you're shrewd you'd use the time spent doing it to establish a publication record, network, do stuff other than academic work etc. I'd also say that if you think you might want a PhD at any point in the future, you're probably best served doing it early. Sometimes people aren't ready and going for it down the line makes sense, but the more you get tied up with stuff the more difficult it is to get back into that sort of thing.

Another quick bit of advice, all other things being equal - American MA, British PhD. If you want to do a stand-alone MA as a terminal degree, you are probably well advised to try for an American one, if you can get funding for it. American MAs are undoubtedly better than British ones. They take an extra year, but you'll cover a LOT more ground and you'll do a proper thesis. The flip side of this is that if you want to do a PhD, you're better off doing it in the United Kingdom. As long as it's from a top university, the final qualification in terms of research is just as good, it takes less time and there are fewer peripheral hoops to jump through.

Also, if you begin to incline toward a PhD and can't get a scholarship for it, you may be best advised not to bother. You'll bleed yourself dry and sometimes potential employers take PhD funding to be notable by its absence when they look at your CV.