CO and virgin atlantic VS had "hard" codeshares in the iad-lhr route. CO bought the seats. exact seats, like in 5 AB, DF. etc. once they owned them they sold them as best they could, independent of VS, the operator of the plane. on two occasions, My wife and I purchased "upper class" tickets(considered more or less first class by VS) but sold as business class tickets by CO for slightly under $1000 rt about 3-4 years ago. they came with all the VS UC frills, excluding the limosine trip to airport.

we were also able to exchange seats into VS seats(row 1), once at the airport.

I do not know if this hard codeshare still exists, as I no longer have business in london, so no longer travel there.