I've said it before and I'll say it again: bugger bog gardens. So here's my proposed methodology for getting the drainage functioning:
- excavate the remaining brick and timber subterranean terracing on either sides of Old Greenhouse;
- clear topsoil from the Old Greenhouse area, (hereinafter The Pond) by throwing and barrowing it onto the beds;
- excavate the greenhouse foundations from The Pond;
- excavate The Pond, 3-4ft deep, 10x20ft in area;
- puddle the same;
- lift flags, and dig trench under northern end of path - make sure it's acting like a wee stream, water running off beds into trench, and then down into The Pond;
- dig trench northern end, ditto;
- fill both trenches with bricks;
- relay flags on northern path;
- construct bridge across pond;
- bloody hell, voila.
Lots of work: lots of endorphins released and calories burned. Also, the vast quantities of bricks being unearthed will put to good use, (taking them to the skip in the barrow would be almost as much effort).