That's just one clause
The agreement between BBC Worldwide (the commercial arm, not the Auntie Public Service Broadcaster), and Flextech (the content/channels arm of the former Telewest) over their joint venture channels (UKTV) has various clauses like this in it. First refusal at buying if the other partner wants to sell is just one.
IIRC - when NTL wanted to buy up Telewest and form a single UK cable company they had to do so in such a way as to avoid a change of control of Telewest as that would have triggered another part of the pre-emption clause in the agreement allowing BBC Worldwide to take control of the UKTV channels in the joint venture. As NTL was bigger than Telewest this was a PITA (for NTL and Telewest), as rather than a standard take over of Telewest by NTL they had to structure the deal so as to avoid triggering that change of control clause. At the time having a content business was seen as being beneficial to the enlarged NTL. Oh how times change!
AND the clauses in this agreement work both ways. This may not have been significant at the time, but now the gubberment is talking about forcing a part-privatisation of BBC Worldwide and/or merger with Channel 4, this becomes relevant to VM as it could be painted as a 'change of control'!
I might be too late with this comment - I think all the WWDC10 and J-Phone stories have pushed this one off the front page radar.