Been reading through this thread as it been quite a nostalgic trip seeing the old Ondigital and Telewest screen shots again
Cable & Wireless were the first to launch in 1999. the initial CR1 software was developed by Pace and used an
EPG developed in C with the liberate browser being tacked on separately. This meant when you pressed the interactive button you had to wait whilst the Liberate browser loaded. The CR2 and later software would be based on Liberate 1.2 and would integrate the liberate browser within the guide. The original smartcard mentioned was yellow and had a large green traffic light that said GO!
ntl went a slightly different route, whilst the initial CR1 guide was developed by Pace they had planned to use PowerTV for the middleware rather than Liberate, but dropped it when they merged with C&W which explains why it took so long to launch interactive on that platform. They had also planned to launch a proper internet tv service similar to Microsoft Webtv or those Bush internet tv's but by that point the world had moved onto HTML4, the Liberate software only supported HTML3 without CSS. Also looking at the software changelogs on Digitalspy, at some point the guide information was transmitted via DAVIC which ntl called an iEPG, I guess the channel data is stored with the DVB tables/NIT, whilst the program guide listings was transmitted via IP. By CR2 this changed to traditional DVB for all aspects of the guide. The Di4001 boxes used does not require a Net id to startup, as it will scan and set its own Netid.
Regarding the differences in channel numbers, ntl originally grouped the channel number by package, which would explain why some mainstream channels here in the high 800/900s, however they also allowed you to change channel numbers manually which indicates that they are stored in the STB's flash somewhere. They dropped that feature when they merged with Telewest, along with the 3 day tv guide.
Telewest mostly just copy and pasted Cable and Wireless implementation, the CR1 software is the same in concept with the Liberate browser being a separate component. Again they adopted Liberate 1.2 and rewritten their guide software. Strangely the Cr1 software had certain features disabled, such as the volume control, when you attempted to adjust the volume on the box a message popped up telling you to use your TV remote control. CR2 fixed this and was even promoted as a feature on one of their information channels. The only other difference is that Telewest had used Scientific Atlanta boxes like the 4000dvb and 4200dvb which mostly used the same chipset and firmware as their Pace counterparts.
When VOD (Teleport) services launched, a lot of the middleware had changed which may explain why later post VOD software has issues starting up, I believe they are reliant on a return path being present and won't operate without it to stop the use of modified set top boxes, since a common thing to do was to cut the talkback, preventing the built-in DOCSIS modem from functioning. Another popular mod was to cut the write point on the flash chips to prevent the box from being able to overwrite software which would explain why you still have a box running CR1. Since modified boxes could not access the interactive features, it made since to use an older, faster version of the software. They did change the DVB tables to prevent boxes with the old software from functioning around the time VOD had launched, I'm not sure if this affected CR2 but CR1 was defiantly affected.
There was another provider worth looking at, Smallworld which was also known as Wight cable north and ONME communications. there's not a lot of information online but what I've discovered is they used the same boxes as Virgin used (Pace Di4000, albeit in silver), the same software (the user guide I found mentions Liberate being displayed on the startup screen, which indicates a CR2/CR3 variant) They later rebranded to Smallworld and had switched to Kaon set top boxes. Not sure on the software used.
This isn't to be confused with WightCable, now Wightfibre which is the only alternative cable provider left remaining. I'm not sure what set top boxes or middleware they used, maybe Pace?
Finally there is Kingston which isn't a cable company but was the first IPTV provider in the UK (Although BT were testing a VOD service in 1995, it never launched) and worth a look at. They used a Pace DSL4000 which connected to an ADSL modem via ethernet. I doubt there any chance of getting the boxes to function now, they require active communication with their servers in order to function, I'm not sure if they even boot up. The software I'm not 100% sure but it may have used RISC OS with a front end called ANT which as similar in concept to Liberate. Pace did acquire element14 which owned some ARM properties and had intended to release an ARM based internet tv. This evolved into the Bush internet TV.
One piece of useful software to look out for is Libdebug, sometimes known as 'libby'. This was a debug tool used by Pace to test and load firmware onto their STB's that was leaked and had been used to extract the boxkey from the firmware. It was originally for analogue and later digital cable boxes, but not Sky or ONdigital boxes since they use a different debug toolkit. You may be able to connect via RS232 and see any debug output of when the STB is booting, which may help to see that the STB is looking for.
Sadly I reckon a lot of the old interactive content is lost, unless it's sitting on an old Virgin Media server somewhere