My engine has done at leat 50,000miles (don't ask why I don't know) and was using a fair bit of oil when I used putoline 10w40 cheapo version (not sure if semi synthetic or not).
I then swapped to 15w50 and the oil consumtion is less than half, i can't remember if it is fully synthetic or semi. The dealer at the time said it might make the clutch slip - they all say that! But the makers website says it won't and it doesn't. In fact although more expensive it saves me money as I don't burn much of it, but using the cheapo stuff I found it broke down faster and the consumtion got higher between the 4k changes towards the end.
I'm in central Scotland, so I'm riding in similar weather to you (dull, damp, dreary and dreicht, but at least the winter's better)
I use either Castrol 4T or Halford's 10W-40 Motorcycle oil (Bugundy container)
I'm not using any oil between changes.
Some people have reported that when switching from mineral, or semi-synthetic oil to fully synthetic that they do get higher oil consumption, and that by switching back again the oil consumption drops.
So it all depends on what your engine's been used to.