I've been London commuting for the last 19 months on a Triban 520 Flatbar which has standard metal pedals with half toe clips without the straps. Also not wishing to go the clipless route I started with a standard pair of trainers but then switched to a pair of Karrimor Summit walking shoes which I already had and found them to be ideal. They're quite low profile as far as a walking shoe is concerned, so fit into the toe clip easily and have a grip on the bottom so dont slide around on the pedal. The metal pedal finally wore a hole in the sole and have now replaced them with the same in black - only £29.99. These ones have a more rigid sole than the previous which seems to hold your foot in place better.
https://www.sportsdirect.com/karrim...3R6klJbEZToJS6UeEZsgxQKVv1ga48ZoaAi_REALw_wcB.
https://www.sportsdirect.com/karrim...3R6klJbEZToJS6UeEZsgxQKVv1ga48ZoaAi_REALw_wcB.