You can only record ITV programmes from live broadcasts on 103, if you watch on catch-up it's not live and will connect you to ITV-X so if you have the mega package you can't fast forward it would seem, your best option would be to set a recording if it's something you know is coming on and want to watch, if it's something you have just seen on the TVGuide and have missed then the catch-up ITV-X option is the alternative with adverts and no fast forward, probably similar to other catch-up channels.
I always set up recordings for programmes I know I want to watch rather than using catch-up, some channels have programmes showing catch-up but it disappears not long after the programme has finished.