I posted something similar not too long ago.
Nice rim brake road framesets – what’s left?
At the time (I don’t think I saw Paton’s list near the bottom) I decided that the Bowman Palace 3C would be my personal choice, although there were some Ridley framesets kicking about that looked ideal as well (you could buy Heliums as complete builds and punt the bits you didn’t want possibly).
In the end I never went ahead with it, I don’t think my current frame is old enough to justify replacing and I could use the money to better effect building a new gravel bike.
Also, I think Basso framesets are available in the UK, the Vento comes in a lovely shade of blue and fits your requirements?