I have real problems getting ITV and Channel 4 on Freeview. Does anyone else have this problem?

Sounds like your aeriel isnt picking up multiplex 2 see this link.

http://www.dtg.org.uk/retailer/dtt_channels.html

Im not technical but your aeriel may not be positioned correctly or you may be in a poor reception area for this group. How old is your aeriel?