It's a big shift and you should start by considering what you regard as "success".
Will the new path allow you to reach this goal more quickly, or will you just be resetting your "scorecard"? You mention that you feel managing 4 people is limited personal responsibility - if you want to have control over a large number of people then a front-line team leader position is the best place. In consulting and MBA-manager positions, you will manage 0 or maybe 1 person, and you will have no direct control over others.
Some research suggests that people are most "happy" when they are doing what are good at - to be the biggest fish they can in their own pond. Would you prefer to be a good technical team leader, or a mediocre consultant/manager?
It sounds like the general management track may not even be your first choice, as you mention you would have liked to try specialised consulting if it wasn't for your age. There is a big risk that you will be just as disappointed with your management career track, and will have "thrown away" even more time. It often seems that the "grass is greener on the other side of the fence", but even (especially?) general managers and consultants have many worries about whether they are achieving anything significant in their jobs, or making sufficient progress.
Of course, if your goal is to try many things in your life and you are not worried about money, external recognition or promotion, then a distance-learning MBA makes a lot of sense. It will allow you to try a few business subjects without committing to leave your present job immediately. The brand of the school is less important as you have other qualifications and most importantly, work experience on your CV. However, the two schools you mention do offer good programmes. You should also look at the Open University and the Manchester Business School distance learning MBAs as these are perhaps more likely to have people with your background (more mature students with previous management experience and scientific/academic backgrounds).
The main benefit of the MBA may be to demonstrate your commitment to a career change. You are likely to be most attractive as a candidate to scientific and chemical companies who will like to leverage your PhD experience as an "interface" between business and technical groups. If you want to move into something completely unrelated (e.g. advertising), the MBA will also help, though it will obviously be harder to sell yourself as your PhD and prior experience won't count for much.