Nottingham is generally more respected for economics than Manchester. However, the course at Manchester (which requires A-Level Maths) is obviously going to be more mathematical in comparison to the BA at Nottingham. L102 is therefore perhaps more suited for a career in IB.
An undergraduate in Industrial Econ at Notts (john_williams) told me that a number of people in the 2nd and 3rd years have successfully secured internships, but I don't think he mentioned any IBs. It may very well be the same case with Manchester tough. It's a tricky one- I would go with the course structure that you prefer and equally the university that you believe you can make the most of.
Out of curiousity - what is the difference between L102 and L100 at Manchester?