Lovezzin covers it pretty well I think - my only slight disagreement would be that the graduate schemes do make it much easier to make CEng, and that BEng+MSc is at-least as good as an MEng.
I did the graduate training scheme thing (not recently!) and it is something of a double-edged sword. The employer wants to train you to fit a nice convenient cubbyhole somewhere, but on the other hand they have to give you a broad base of experience to keep Eng.C/RAeS happy, and you can with care milk that very much to your own benefit. There's little to actually force you to stay there unless they give you the jobs you want and once getting towards CEng status you're very employable.
There is a risk of becoming over-specialised, but if you chase the stuff you want to do, and use what you got out of your degree effectively - you can do pretty well.
The odds are you'll never make it rich mind you, but neither are you ever likely to either feel hard up or bored. It is all about getting to play with lots of big toys!
In 20ish years since I kicked off I've clocked up a lot of flight testing, time working on an aircraft carrier, supersonic wind tunnel testing, managing big and small flying labs, overseen approval of whole aircraft designs, designed bits of aeroplanes, occasionally put overalls on and worked on them, written a book, appeared in court as an expert witness, managed small and large times (and nobody at-all), travelled to 20odd countries for work, taught from BEng up to PhD levels. I'm having great fun and whilst the BEng is ***** hard work (as was the PhD I followed up with a few years later), wouldn't have had half as much fun without.
G