Garden/Garage drainage

[Su2402#]

Ideas for drainage please. Back garden has patio and raised (currently gravel soon to be turf) garden. The garage has a trench all way round garage that doesn’t drain fast… retaining wall built on slabs around edge of garage so not easy to break these..water ‘table’ seems high as in between slabs of patio the water also hangs around… nearest surface drain is round side of house.. neighbour has a manhole this is edged with bricks under cover… then we have concrete from there to our garden.
Currently planning to try and break slabs a little to dig down and fill with gravel (clay is under here) & stick membrane on external garage wall and back fill trench with gravel and then mud.
Any ideas of drainage or better idea than what we currently have planned? Pics to help show issue

 

[Su2402#]

Images here to give idea of issue

 

[jj4091]

Not a builder but looking at your pics. I would be tempted to just get a big sheet of DPC line the whole area between the garage and retaining wall level with the top of the retaining wall and fill it with gravel to create a large soak away.