Thanks for the advice, since the post and responses I have spoken to a few builders and taking all on board.
I will wait until dryer/warmer, then will dig out the trench to just below kitchen floor level and put in some waterproof concrete at a slight angle to enable drainage from bottom of trench past the lower part of the retaining wall.
For the external kitchen wall, once trench dug allow the bricks/wall to dry out before applying a waterproof membrane. Then place on the bottom of the trench and extending up to close to top of the external wall Pond lining as another added waterproof layer. Fill the drench with small stones with a drain pipe at bottom of trench to ensure effective drainage
Hopefully problem then solved (fingers crossed)