Ok, this box is used by Time Warner, Comcast and Verizon and is found in 95% of homes that have an HD TV set.
I've marked the connections, the layout should be similar on your cable box.
And this is a picture of the Back of YOUR TV set. Match the Red to Red, the Green to Green and the Blue to Blue, then finish up with the AUDIO connectors.
Now if you aren't using one of the SILVER HD cable boxes, and you actually have one of the BLACK Boxes and it does NOT have the word HD written on the front of the cable box, then let me know, ok? I rarely find an HD TV set connected to a Low Def Cable box anymore.
Also, if you are actually Living in the UK or some other European nation, then that would explain WHY you have no Green Connector on the Back of the Cable box. The Irish took it, and they won't return it until later next week....
In the USA we use Yellow-White-Red connectors for Low Definition Cable, and we use Channel 3 for it too.
We use 5 wire Component connections for HD pictures, and the Red /Green/Blue Video connections do the same thing as the OLDER Yellow one did for 25 years.
So double check those connectors, if you have a BLUE one, that logically means there is a Green one teamed up with it....
If you have any questions, just ask