Multiplex A was allocated to S4C, the Welsh language broadcaster.
Multiplex B, C and D
These were allocated to British Digital Broadcasting, later known as ONdigital and ITV Digital. These were to be used for "pay TV" services. These multiplex originally ran in 64QAM mode, delivering 24Mbps.
After the failure on ITV Digital, their multiplexes were put up for auction.
Multiplexes 1 and B
Multiplex B was then allocated to BBC Free To View Ltd (BBC FTV). The BBC switched multiplexes 1 and B to 16QAM mode, delivering 18Mbps each to provide more reliable coverage but with an extra 12Mbps.
Multiplexes C and D
These were awarded to Crown Castle International (CCI), which was originally part of BBC Engineering that was "liberated" from the BBC by the 1996 Act. These multiplexes were also switched to 16QAM mode, with 18Mbps each.
Ofcom frequency negotiations
The Ofcom international frequency negotiations for the digital-only terrestrial television used new designations for the multiplexes. These were:
Multiplex 1 - PSB1 ("Public Service Broadcasting")
Multiplex 2 - PSB2
Multiplex A - COM4 ("Commercial")
Multiplex B - PSB3
Multiplex C - COM5
Multiplex D - COM6
To distinguish the multiplexes in the switched-over regions from the original ones, Ofcom now uses these names:
Multiplex 1 - BBCA ("BBC A") - back in 64QAM
Multiplex 2 - D3+4 ("Digital 3 and 4 Ltd")
Multiplex A - SDN ("S4C Digital Networks")
Multiplex B - BBCB ("BBC B") - - back in 64QAM
Multiplex C - ARQA ("Arqiva A") - back in 64QAM
Multiplex D - ARQB ("Arqiva B") - back in 64QAM
Arqiva bought Crown Castle International.
Freeview HD will provide, from 2 December 2009, a new service on Multiplex BBCB. This will be in 256QAM mode.