does anyone know if either John Lewis or Marks & Spencer in Reading UK have wheelchairs one can use ?

Answer 1

John Lewis does, although they advise to contact the store to check availability. Here is the Disabled facilities page for John Lewis, Reading

http://www.johnlewis.com/Shops/DSTemplate.aspx?Id=80

No info on the M & S site, but here is the link for the M & S Reading store
http://www2.marksandspencer.com/thecompany/our_stores/details.asp?client=mands&db=pc&width=200&height=200&scale=1&prno=1+%21%3D+-1+AND+1&product=&coordsys=&store=8&namepart=&pc=&productrange=

Answer 2

Why not call them & ask?