I noticed on Twitter in the past that BBC SNG trucks have the prefix UKI. Correct me if I'm wrong but I'm guessing UKI is an acronym for United Kingdom and Ireland?
Just United KIngdom - Irish dishes are prefixed IRL.
Transportable Earth Stations are generally country code + number, Fixed Earth Stations are country code + sitename + number. The BBC's main national trucks were the 'triples' - UKI-777, UKI-888 and UKI-999 - you may have occasionally seen their colour bars slip out on air - though I'm not sure if they've been replaced with recent upgrades. TV Centre's dishes were UKI-TVC1 up to about TVC13. When you get a big event (like a general election) which uses a lot of trucks, then it's not uncommon to see bookings from trucks prefixed F, E, D and DNK.
The point of them is so that you can identify yourself when lining up a transmission. Satellite space is tightly controlled. Each transponder will be leased out to a broadcaster or telco for fixed or occasional use, and with occasional use (ie ad-hoc transmissions), it's very important to check everything's right before bringing up a carrier - getting it wrong could interfere with other transmissions, or at worst, damage the satellite. That means the uplink operator has to call up the satellite operator, identify themselves, the channel they want to access, and be 'talked up' onto the bird - initially with an unmodulated, reduced-power transmission, to reduce the chances of interference in case the transmit chain is on the wrong frequency.
For Eutelsat's satellites, then their own CSC will do the line-ups, but if the company leasing the space is considered to be competent enough, then they can do their own line-ups: so the BBC's leased space on Eutelsat 7A and 10A are managed by their own Satellite Operations department.
Here's a pdf with more information than you probably wanted about satellite line-up procedures