Can my old landlord open my post?

Section62

RHemmings said:

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I'm not saying that it's legal or illegal to open mail addressed to your address but to a different person. However, when I try to check the facts I will say that the opinion that it is legal is a minority opinion, and the majority of the opinion I found including from the most reliable looking sources I can find says that it is illegal. 

When fact checking legal issues what matters isn't the number of people saying something, rather whether what they are saying is backed up in law.

In this case the law is clear, though clearly misunderstood by people, many of who ought to know better.  That a council employee thinks they can get someone arrested and charged for opening a letter correctly delivered to their address (your LincsOnline link) demonstrates the point well.

FreeBear

Section62 said:

RHemmings said:

....

I'm not saying that it's legal or illegal to open mail addressed to your address but to a different person. However, when I try to check the facts I will say that the opinion that it is legal is a minority opinion, and the majority of the opinion I found including from the most reliable looking sources I can find says that it is illegal. 

When fact checking legal issues what matters isn't the number of people saying something, rather whether what they are saying is backed up in law.

And when it comes to interpreting the law, the definitive source will be high court & supreme court judgements.

General_Grant

BobT36 said:

Ask them not to open your private mail please, and to batch up and forward anything addressed to you onto your new address (compensating them for the stamp cost), go over to collect it, or return to sender. 

They don't need to "batch up" and pay postage.  They can simply cross through their address (so that it is still legible, not totally obliterated) and put on it "moved to" and the new address and put it in a postbox.