UK Sewage connection - is an external rodding point mandatory
Approved Document H says:


  2.46 Sufficient and suitable access points
  should be provided for clearing blockages from
  drain runs which cannot be reached by any
  other means. The siting, spacing and type of
  the access points will depend on the layout,
  depth and size of the runs.


There is nothing to suggest that the access points need to be external.