In a bid to tackle piracy, the watchdog has approved the broadcaster's request to ensure only devices with content management technology - which prevents programmes being copied to discs - will be able to access the broadcasts.
"In response to a public consultation on this issue, the BBC, ITV and Channel 4 provided evidence that without a content management framework in place the range of HD content available on Freeview - in particular high value film and drama content - would be compromised."
"This technology would control the way HD films and TV shows are copied on to, for example Blu-ray DVDs and shared with others over the internet," added Ofcom.
Brits will still be able to record HD content to their digital video recorders. Furthermore, standard definition content will not be affected.
Ofcom also said the BBC had to guarantee to deliver net "benefits to citizens and consumers by ensuring they have access to the widest possible range of HD television content on DTT".
However, the Open Rights Group called the move "a serious blow to UK consumers and licence-payers".
"They have taken a decision which pushes technology further towards a copyright-centric model of control, where only copyright holders have the right to decide how everyday devices are allowed to work," executive director, Jim Killock, said in a blog.
See also: Freeview HD officially launches today