shimano M545 left pedal cap unit bolt fallen off during use
Wiggle will do you a refund as well as a replace. There should be no problem with that as M545's are known to fall apart in the way you describe.  

Sounds like you are looking for a pedal that works well with cleat and without cleat. I do not think the M545 does either job properly, and, as evidenced, can fall apart. They also do not work with some leading brands of 'SPD' footwear.  

I would send them back and upgrade to the plain Time ATAC pedals, also available from Wiggle. These may not work too well with leather soled shoes in the wet, but you can get home from the pub with them and regular trainers without your feet slipping off.  

I have updated the clipless pedal page with my own IMHO on Time Atac pedals:  

What should I look for in clipless pedals and shoes?