Maggots can smell if they get warm and sweat.
If you do buy some from a fishing shop ask for some 'dust' to be put in with them, this is very fine sawdust which absorbs any moisture, and then keep them very cool. Fridge is best if you can bear the idea or outside in a potting shed would do in these temperatures. A couple of extra quid spent on a proper maggot box with air holes will help keep them fresh.
Once Robins find them they can't stay away, I always give them any extra ones I can't use for fishing.