Cult Fix has it on good authority that Merlin will return to British TV screens late September on BBC1.
The fifth series of the show is currently planned to air on Saturday 29 September, a week after Doctor Who concludes the first batch of episodes from its seventh series.
Once again there will be 13 new Merlin episodes in the run and it is expected to air uninterrupted, finishing shortly before Christmas.
Note, BBC broadcast dates are obviously still subject to change up until around two weeks before broadcast.
Well, they also had it on 'good authority' that an actor from a previous series would reprise his role in S5 and it turned out to be a hoax. The reliability of that site (and their sources) is still a bit questionable. On the other hand September 29 is the most likeable premiere date (ep 05.13 would air on December 22).
I'd still not take the article as a confirmation, though, rather a (likeable) suggestion.