There was an antiques business at 52 -  Jonathon Fyson (not Dyson - my typo).  When he died the shop got split into two.  His sister kept a sort of antiques business which you rightly say is Number 52 and the northern half was let to Helen & Douglas House.  Where the map is wrong is that it shows Helen & Douglas House, then south of that it shows Number 52 and south of that The Oxford Brush Company.  Number 54, the Patisserie, between Number 52 and Oxford Brush is missing.