You can do whatever you want with exceptions. Nothing guarantees you a job these days because the job market is bad. There is a surplus of graduates but not enough places for everyone. It is good that you are undertaking a placement because you will end up getting valuable work experience which employers are really looking for. Also, it is possible to be offered a place on a grad scheme after a placement. I know some people that did an internship or a placement and then ended up getting a grad scheme from the same company so it happens.
A masters degree is not required and a waste of money in my opinion. The main problem with universities is that they shove you with a lot of random crap that you're probably never gonna use and forget about afterwards and they also don't provide you with skills that employers are looking for at a satisfactory level. You know, you can be the smartest and good at exams, but have never really worked in a team, or never done anything in spare time. So if you finish BEng with a placement year then you should be okay applying for grad positions. A masters is not needed.