HNC/D are technician qualifications, which means, 9 times out of 10 you'll be drawing up someone else's design or picking up all the little jobs that no one else has time for. These will get you Eng.Tech and IEng (about 5 yrs for IEng; 2 if you get lucky with your portfolio) membership with the institutions but without about 10 yrs working experience, they'll just be fancy titles to employers.
The B.Eng will get you a better starting wage and you'll start as a junior design engineer, rather than a junior technician and your starting projects will be a bit more involved than a tech's projects. With a good push you can qualify for C.Eng, meaning you can sign off your own and others work. More responsibility = loads 'a' money. Or great power. Or something.
You could go for careers in: oil & gas, HVAC, process machinery design, pipeline engineering, R & D (with good experience), thermal engineering and pressure vessel engineering. With the right supervision you could also cross into structural and temporary works.
That is in no way a complete list. There is loads of specialist and niche sectors you could move into.