Thanks guys.
The filter is fairly standard ideas, actually out of date by most standards! The real innovations, IMHO, are builing it out of concrete and the sump chamber to allow me to re-use all the water. Having said all of that, I wouldn't build it the same again! I'd learn how to build my own chambers from glassfibre and make them out of that! I'd also completely change the pond design so it's better for keeping koi, but probably less ornamental. However that's a different type of pond really! The changes I'll be doing in half term probably will be a big step forward too, both in improving the water quality and making it even easier to clean! I may even add another filter...