Pros
Salaries are generally good. Lots of money to be made in Quality Manager/Finance Manager/Manager of Projects type roles if you're into that type of thing - they contribute little to the quality of work done but result in huge overheads (a few extra quid for you if you're an ex-army type). If you are a bright and aspiring engineer then I would advise you go elsewhere, if you're a middle of the road engineer from a low-middle ranking university then you'll do well.
Cons
See above. There is little interest in doing engineering work - managers happy to sit on their laurels and take their salary. Don't be fooled by the size of the company and management speak and their claims to have worked on fantastic projects - if they can farm you out to a utility company on a 5 year framework they will.