Cool combo structure!
One tip though; try using gravity connections for the timber frame (e.g. pinkbike.com). The way you have built it most of the force is taken up by the nails which is a lot less efficient.

 Thanks! Its hard to tell on this photo, but the beam nailed to the side of the posts is sitting on a ledge that we notched out so the timber will take the load. I'll adopt gravity connections for the next build though...

 nice!! iff the forestry commission found that sort of stuff up our local woods they would have kittens!

 Thanks, the land is privately owned so no FC involved. We try to keep everything big enough to keep the kids off too!

 How longs it taken you to build this bit?