Your school are probably trying to maintain their own reputation getting as many of their students into top universities as possible - it might be a statistic which they care about for telling parents what a good school they are, to secure their funding, and their place in the rankings, etc. None of those things are any of your concern. In this case I wouldn't necessarily assume that they have your interests at heart.
You will also find some people have a very over-inflated opinion of what it means to get into a Russell Group university, and while going to a high-ranked university is generally positive for a lot of students who get there, it's certainly not the high-water-mark achievement that some people like to believe, and it doesn't automatically lead to success later in life either. On the other hand, the apprenticeship you've been accepted on to sounds like a great opportunity to get training in a high-skilled engineering job; realistically speaking those types of jobs are far more dependent upon skills and experience than your educational background.
Also, the option to go back to full-time education will never be closed if you decide that you'd like to study something later on in life, so you have nothing to lose by accepting the apprenticeship.