iPlayer is currently a maximum 3.2Mbps 720p 25fps using AVC / H.264 encoding. BBC 3 via cable was 1080i 50fps using MPEG 2 - no idea of the average bitrate, but think was said before that BBC on VM is higher than Freeview or Freesat even accounting for the different encoding.
According to,
http://en.digitalbitrate.com/dtv.php...live=9&lang=en, BBC 1 on Freeview averages 5Mbps with a max of around 14Mbps with AVC / H.264 encoding.
So yes, not as good as broadcast.