OK job half done. Lets just get a couple of things out the way:
1. JCB - there's no way on gods earth you can unblock either drain hole without removing the battery, unless you have a guided drain hole seeking screwdriver which is infinately flexible. The battery sits on a metal tray right over the top of the drain, this has to be removed as well as the battery.
Remove the splashguard first (under the wipers) otherwise it's impossible.
2. There are no pipes or hoses under the grommet, it just drains (or not) directly onto whatever gubbins is underneath it.
3. The grommet behind the servo is shared with some other small drain pipe, so better left in place.
4. The grommet under the battery needs to be removed as mine wasn't blocked with leaves, crisp packets or small children, just plain silt. And still after 2 days of no rain had a good inch of water sitting over it.
the grommet is definately the problem as it only takes a very small amount of silt to block it up completely due to the fact that it looks like this:
Designed purely to get blocked up as far as I can see.
Here's the hole minus the blocking grommet:
Tommorrow the carpet comes out - oh what fun!