Just purchased this tiny ficus (from RHS Wisley) and because the roots are coming through the base, thought I would risk repotting it now (end July in UK).  Or should I wait until August/September - or later - please?   Would really appreciate some advice - many thanks. 

Roots growing out of the pot is not an issue. If it where all my shohin trees would be in big problems. Just remove the roots, that is what I do 4-5 times per year.