Came across this press release from Smulders that explains the "big tubes":
"Last week, the first TPs for the EnBW He Dreiht project were transported from our yard in Hoboken to Newcastle. At our Newcastle yard, we’ll do the outer welding, coating, and final assembly of the TPs.
On behalf of EnBW the joint venture Sif Group-Smulders is manufacturing the 64 transition pieces for the EnBW He Dreiht offshore wind project. The TPs will be up to 30 meters high and close to 8.5 meters in diameter. Each TP will weigh more than 700 tons, including secondary steel."
Still non the wiser unfortunately - wonder what a TP is?

You've spelled it out Dave - Transition Piece - presumably between the seabed structure and the wind turbine tower.

Smulders this afternoon (16/11/2023) and the big tubes, or transition pieces, are now vertical and painted yellow.