I had a separate flight on BMI to/from Dublin-London this summer when I came over on Aer Lingus. It was like $250 cheaper. Well, I didn't realize that BMI was a low cost airline (no orange on their website so it looked like a regular one! :p) and had to beg the very grouchy, b*tchy ticket agent to allow me to check my regular over weight 2 bags (their limit was 1 I think) and rearrange things in my carry on. She grudgingly let them through. I was lucky on the way back, too, and the lady in London was able to check them even though they were over weight. I just told her that I was there for 2 months and flying internationally once I got to Dublin. You never know.. they might be understanding even if it isn't strict policy.
