I am a landlord, and a previous tenant of mine has left the property. They have left piles of black bags in the rear garden and in the property. Some of the bags contain letters that have been opened. Can I read these letters?
According to the Torts (Interference with Goods) Act 1977, any possessions left in the property after the tenants have vacated still belongs to the tenant. You are obliged to inform them that they have left some of their possessions behind and you can bill them for any expenses incurred in the disposal of it.
In terms of reading someone else's mail that has been opened you may be liable under article 8 of the Human Rights Act 1998, since you are possibly accessing your former tenant's personal information without their consent. However, the specifics of the fact that the mail has been abandoned without care does mean that would an interesting legal matter for the courts.
Unless you have a very good reason to read this mail, I would suggest you contact the former tenant informing them that it has been left behind, and if (as is likely) they claim it's just rubbish, then dispose of it and send a bill to them.