It would be useful to know the make and model number of the DVD recorder. Some of the earliest models didn't have any TV tuner built into them. (You needed to provide the signal to be recorded from an external source). However the presence of an aerial socket suggests that your father's DVD recorder must have some sort of TV tuner built into it.
The next phase in DVD recorder production provided each unit with an analogue tuner. I suspect that's what your father has got now. If so he'll currently be able to record from the five terrestrial channels, while watching any digital channel, but he won't be able to record any digital TV programmes (unless, possibly, he can record the SAME programme that the TV is displaying, by taking a signal from the TV's digital tuner).
The third phase of DVD recorder production put a digital TV tuner into each unit (sometimes alongside an analogue tuner).
If your father has got a DVD recorder with only an analogue tuner in it, then he needs to upgrade. If he's got one with a digital tuner in it, he doesn't need to do anything.
Chris