It should be able to record from an external source too, but the TV won't work as an external source (and even if it did it would be a pain to use because you'd need to leave the TV switched on and on the channel you want to record all the time)
The manual is here, recording from an external source starts at page 39 and a cheap freeview box will cost you about £20
ftp://195.35.123.32/CCFTP/Manuals/DVD/RECORDE
R/RDXS24/RD-XS24SB_Ope_E_1121_Rev.pdf