I am not sure what I tried to do really worked - but this is what I did my TV has a split screen so I put HD (?) one one half & the same channel via freeview ( it was bbc1 & bbc HD putting out the same programme) on the other could not see any worthwhile difference .
Then I switched between BBC 1 & HD again nothing to get excited about,
Emperors new clothes comes to my mind.
No way will I pay out another £7 per month
