Almost all the other channels that have "+1" time shift channels are single national broadcasts. It is straightforward to create ITV2+1, for example. The output of the channel is fed into a "black box" that re-outputs the content an hour later, and used for a national broadcast.
As the streams for UTV+1, and STV+1 are now on satellite, we can be confident that the ITV+1 service will run throughout the UK.
Channel 4 plus one
It was a little more complicated for Channel 4. This commercial channel has no local or regional editorial content, but does have six regions for advertising: London, Southern England+Wales, Midlands, North England, Scotland, Northern Ireland.
To create Channel 4+1, the corporation needed to use six "black box" devices, to ensure the correct advertisements are seen.
Channel 3 plus one
Back at channel 3, the ITV1 channel has many advert regions. STV, which runs the channel in Scotland, divides into four:
This requires, for each region, a separate "black box". These "black box" devices must feed the hour-delay signal back into Multiplex 2 (also known as multiplex PSB2) as only this multiplex has the correct regions.
ITV1+1 on screen graphic.
Latest ITV multiplex allocations
The slot on PSB2 currently used for the ITV2+1 will be used for ITV1+1. ITV2+1 will move to the slot on multiplex A (aka COM4 or SDN) currently used for the "ITV Preview". As this slot timeshares with the CITV children's channel, ITV2+1 will only operate during peak hours.
Public service transmitters
As the public service transmitters carry only the PSB1, PSB2 and PSB3 (HD) multiplexes, this means that ITV1+1 will be carried to all UK homes, and ITV2+1 will only be available to those with the full Freeview service.
Free to air satellite
Freesat users will see ITV1+1 (or STV+1 or UTV+1) on channel number 112. For ITV1+1 fSfS and Sky use channel number 131, ITV2+1 moves to 179.
On satellite transponder 53 (10.891 H) has UTV+1, ITV1 Central West+1, ITV1 London+1; transponder 54 (10.906 V) has STV West+1, ITV Granada+1, ITV 1 Merdian South+1.
Channel 5 plus one?
So, what of FIVE+1? The channel has four advert regions: Scotland, Northern England, London and "Network". However, there is no space on multiplex 2 (PSB2) for such a channel, and no other multiplex has the correct divisions.
Any further questions, please contact ITV on 0844 881 4150.
Josh: the problem is down to the law surrounding digitalterrestrial broadcasting. Mux 2 (also known as PSB2, D3+4 after switchover) is required to be licensed to a consortium of Channel 3 companies and Channel 4 Television Corporation, and it may only be used by them to host channels run by Channel 3 companies (ITV plc, STV, Ulster TV, Channel TV) or Channel 4. They are required to host Five (main channel only) and, in Wales, S4C.
ITV plc runs multiplex A/COM4/SDN (bought from S4C in 2005). Arqiva run multiplexes C and D. For competition reasons - since ITV is a broadcaster and Arqiva owns the masts - they are not supposed to discriminate against channel operators, operating free auctions when a slot becomes available. They're certainly not supposed to force out existing channels. The regulator plays no part in deciding what channels are available on the commercial multiplexes.
Freeview Limited is just a marketing company, co-owned by the BBC, ITV plc, Channel 4 Corporation, BSkyB and Arqiva.
ITV plc *could* move ITV4 to D3+4 in place of ITV1+1. Channel 4 could move Film4 or 4Music in place of C4+1. This would free space on Mux D (COM6/ArqB) for more channels, but they would then be auctioned to the highest bidder.
Looking at the BARB statistics, ITV1+1 had already managed a 0.4% share for the launch week, ending 16 January. In comparison, on satellite and cable, the CBS channels you mention only achieved 0.1% each, so you'd think they'd struggle to pay as much for the slot as ITV do - ITV4 got 1.0%. C4+1 achieved 0.9%, Film4 got 1.0% and 4Music 0.3%, so C4+1 is worth nearly as much as Film4 and a lot more than 4Music, and costs fractions of the amount to run.