The media regulator and the BBC's overseer have established how they will work together on the process that will see Multiplex B, currently used by the BBC, cleared to make room for four HD channel slots.
The first three slots will be available from 2009 and the fourth from 2012.
's proposals run counter to a plan put forward by an alliance of the BBC, ITV, Channel 4 and Five that involves the first three taking the 2009 slots and Five taking the 2012 slot.
The plan was proposed in February via the BBC Executive to the BBC Trust, but the trust has admitted concerns that this could mean it was taking on responsibility for non-BBC content.
Ofcom was also concerned about the trust encroaching on its regulation of commercial broadcasters, about broadcasters controlling spectrum allocation and over its doubts about the ease with which the appropriate regulatory consents could be obtained.
The Trust has now said it has suspended consideration of that plan, in favour of following Ofcom's alternative proposals. It has come to an agreement with Ofcom that allows the BBC to take a HD slot in 2009 without having to pass a further regulatory test from Ofcom.
Ofcom has made some compromises, which include leaving the regulation of the BBC's use of its HD slot in the hands of the BBC Trust, since its original proposals.
This leaves the process by which HD slots are allocated to commercial broadcasters in the hands of Ofcom, which wants S4C, as well as the other three, to bid in a competitive process.
This, however, cannot take place without changes to the Broadcasting Act, which Ofcom has asked the secretary of state for culture, media and sport to make.
Assuming the changes are made, the broadcasters will be invited to apply for the first two slots on Multiplex B.
The main criteria will be efficient use of the spectrum; contribution to public service broadcasting; and contribution to the range and diversity of television services in the UK.
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