Wow! A wealth of great information, thank you everyone for your constructive advice. To tackle a few of the points raised:
The condensation occurs mainly on the glass, however I did notice yesterday that there was a little moisture on the frame itself so I suppose it's safe to say that the oak is more thermally conductive than the uPVC with it's air gap.
The house has been well insulated and sealed during the renovation process. It makes absolute sense that the moisture that would otherwise have been condensed onto walls, ceilings and floors is now getting concentrated on the windows which will be the coolest surface in the room.
Most of the condensation occurs overnight on bedroom windows. I didn't know just how much moisture we humans exhale into the atmosphere, that was quite a surprise! We always keep the bedroom doors ajar during the night but clearly this doesn't provide for a circulation of air adequate to remove sufficient moisture from the room to prevent condensation occurring.
I am kicking myself somewhat because during the renovation process we had planned to include a whole-house ventilation system with heat recovery. Sadly it was axed at the last moment as we just couldn't afford it.... ahhh hindsight is a wonderful thing. I could easily add HR ventilation to a couple of the rooms easily enough as they have a roof space adjacent but the rooms that suffer the worst of the condensation do not. I am wondering if I could vent these rooms (either passively or using a low speed fan) into a stairwell. That would be easily achieved as they are separated by just a stud wall.
Jacob, your wealth of knowledge never fails to amaze me. I have never seen, or even heard of, the drainage channels that you suggested. I'll be looking for pictures or diagrams of that system as I am just so intrigued. Unfortunately I think it is too late to add such a feature as the second lot of windows are almost complete.
Prior to us renovating the house it stood empty for over ten years with no heat and little ventilation. The walls are up to 18" thick in places and the local stone is quite porous so I would imagine it could hold a lot of moisture but as they were lined with breathable membrane I would hope that most of that moisture will be lost to the outside, not inside. What I never understood was that if the membrane can breathe surely it can allow the passage of water vapour in the air??
The glazed units were fitted the correct way around - eventually! I did fit the first one the wrong way around not knowing that they had a specific orientation. When I proudly announced to my wife that I had fitted the first window she came to inspect it, started peeling the stickers from the glass and noticed (in large bold print!) words to the effect "glaze with this side outwards". She called me a few interesting names and I retired back to the workshop with the window and my shame
The units are argon filled and we would have had a slightly larger gap but the glazing company advised that rather than using two panes of 4mm glass we should use a 4mm and a 6mm for additional noise reduction (we live by a fairly busy road and noise reduction was high on our list of priorities). The theory is that different thicknesses of glass will absorb different frequencies.
Again, a huge thank you to everyone for the fabulous wealth of information, advice and suggestions. I will have to consider what direction to go from here but I now have a much clearer idea of why the condensation forms where it does and what I might do to combat it. I'll let you know how it goes.
Paul.