Hi there .thanks for that , I had only just clicked that it was a solid tyre .
More info has been provided now

The rim looks to be a hooked ? rim, rather than the dished ones I have seen in the past for solid tyres
hopefully will take a pneumatic tyre ( rim drilled for valve)
I can get hold of 16x1-3/8 which we will try and see .

Thank you for the input