Hi Dave,
You've already mentioned where your problem lies and that's with your portion sizes, reduce the size of your meals and you will definitely see your weight reduce, obviously you will need to adjust your insulin to compensate for the reduced carbs.
When you do begin to cycle to work you may have to reduce your insulin again depending on the duration of the exercise, I eat potatoes, rice, pasta, bread, pulses and fruits but in them all in moderation as part of a healthy well balanced diet, remember if you burn more calories than you consume then the weight will eventually move.
If you haven't done a carb counting course already then I suggest you ask your DSN about DAFNE, it's aimed at type 1's and teaches you to match your insulin to the food you eat, how to adjust your insulin when ill or partaking in exercise as well as many other areas of diabetes management.
Good luck!