I think they might be 24 x 1 3/8.
That size is the British Juvenile on Sheldon:
http://www.sheldonbrown.com/tire_sizing.html
SJS have these (rear only it would seem):
http://www.sjscycles.co.uk/src/froogle/product-Unbranded-Wheel-Rear-24-x-1-3-8-Inch-with-Nutted-Solid-Axle-and-Silver-Steel-Rim-Screw-on-Single-Speed-Freewheel-2936.htm
I definitely call to check though.
@goodhead started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
I think they might be 24 x 1 3/8.
That size is the British Juvenile on Sheldon:
http://www.sheldonbrown.com/tire_sizing.html
SJS have these (rear only it would seem):
http://www.sjscycles.co.uk/src/froogle/product-Unbranded-Wheel-Rear-24-x-1-3-8-Inch-with-Nutted-Solid-Axle-and-Silver-Steel-Rim-Screw-on-Single-Speed-Freewheel-2936.htm
I definitely call to check though.