Play Area, Wet Garden

Hi

I'm looking for some advice. I've a very poor draining lawn, coupled with an excessively wet year that we've had so far in Scotland.
I've decided to build a play area for the kids with the intention of putting in a climbing frame and some playchip.
The area is 6m x 5m, towards the end of the garden on a slope. I've been digging into the slope to try and level it out a bit as probably drops 30 cm over the 6m length. The soil has a large amount of clay throught it, with the remainder being whatever the builder threw into it. bricks, bottles, probably there left over sandwiches.
Anytime i'd digging, if there's any rain afterwards, is sitting on the level of the soil.
I intended to put a membrane down then put the chip on top, but the i thought if it rains the water level will just back up through the membrane into the chip.

Can anyone offer any advice on how to disperse the water. At the bottom of the garden i've an area that I could use as a soakaway if need to route anything that direction.

Thanks in advance.

Danny

Soakaways don't generally work in clay.

Any idea what does work in clay? Garden's aren't really my forte.