I assume that you're using a VCR (or another type of video recording device which incorporates its own analogue tuner circuit), together with a Freeview box.
If you record from analogue TV, the VCR will use its own tuner to convert the RF (radio frequency) to the AV (Audio-video) form which it records on tape. If you want to record digital signals, you have to let the tuner in the digibox convert RF to AV and then feed the AV signal to the VCR.
Connect the Freeview box to the VCR with a Scart lead. (If there's a choice of sockets, use the one labelled 'Out', 'VCR' or 'Record' on the Freeview box. Use the one labelled 'In', 'AV' or 'Aux' on the VCR). Switch the Freeview box to the desired channel (and leave it switched on!). Then set the VCR to record 'AV', rather than any numbered channel.
Chris