Of course you watched the animation out on a good – preferably broadcast quality – video monitor before and after transfer to DV, and it was looking good then …? You really cannot judge video for broadcast from a computer monitor or an LCD.
Assuming it was good from your DV playback, then the DV-DigiBeta transfer would be your next suspect. But really going through DV at all was a bad move. You lose resolution and colour information by going to DV at all, and no mainstream UK broadcast channel’s engineering dept is going to be happy with a DigiBeta transfer from DV.
What you could try is contacting your transfer facility, and asking what computer output that they can handle – frame sequence, or interlaced uncompressed quicktime or avi file? That way you could hand them a full resolution, full quality output file from AE and get full broadcast quality DigiBeta in return.
Some issues which can arise going from computer to broadcast video include:
flicker , which can be caused by field order issues (in PAL, DV is lower field first and DigiBeta / everything else is upper field first), or by single-pixel lines or edges, which always look bad: a little judicious softening of edges will help.
gamma – the brightness / contrast handling can look quite different on a video monitor from Windows or Mac computer displays; and
legal video colors / video levels where AE handles RGB levels 0 – 255, for video that range has to be restricted to 16-235, even after any glows / filters / effects have been added.