I think you'd be better off asking this question in an engineering institution forum as opposed to the student room. I've just grad'd and started on £31k, I know the budget for an engineer at work (FTSE100) is circa £100k, but that includes salary, support network, training, computer to work at, software, heated building, national insurance and pension contributions, travel allowance, etc.
Besides, salary progression is usually your own problem. If you aren't earning enough working for an engineering firm after 5-10 years, go work as an associate for an Investment Bank/Hedge Fund, or if you don't want to do that, do consultancy, or start your own business. If you have the right skills and experience, you could easily get to the highest tax bracket.