Subsidence or nothing to worry about?

Not particular major if its took over a 100 years to get like that, may just be an issue with the lintel giving a little (if there is one) or the door frame shrinking, fill in and repaint

 

Agree with Severen. But do get a full structural survey by a qualified and accredited surveyor and not rely on a valuation assessment commissioned by the lender.

 

The reason it has cracked there is because whatever is supporting the door opening has moved a little. Like the others have said it's best to get a structural survey if you're unsure. They often used timber above doors and that can change shape over time.

The other thing you can check is whether or not it is a 'supporting wall'. i.e. is the house reliant on that wall to keep the roof or upstairs floors from collapsing? We have two internal walls running down the middle of our house which are just lathe and plaster because all they do is separate the bedrooms from the hallway and they have no structural function. Those walls could be completely missing from our house and it wouldn't make any difference to the structural rigidity of it.

i.e. if it's not a structural wall then who cares!

 

Does the door still fit the hole, check diagonally to see if the door is square or if it has been shaved off before, this will indicate a history of movement. You have to look at the evidence to try to read the history of this movement, is it new or has it continued for some time before you owned the house. Is their a door above or below this door, does that suffer similar issues.

 

As has been mentioned, get your own independent surveyor, same with damp.
Yes it’ll cost you, but the ones that the estate agents will suggest that give a free survey, are generally free for a reason, I.e they will pile on the doom and gloom and often give a report for unnecessary works...especially when it comes to damp.

I bought an older house a few years back which had similar issues, but I knew that there was nothing particularly seriously wrong with it but had to jump through the hoops because surveys were requested by the lender. Paid about £500 in the end for 2 independent surveyors, who both new old buildings and were helpful and user friendly.

The upshot was I renegotiated the asking price and saved a good few grand.

 

Old houses move about over time. I suspect something has shifted here a little bit, but as to how serious it is you will have to dig around and take a view. I am going to guess the door has shifted relative to the floor in some way, as the door has rising hinges fitted - I bet it didn't start off with those when the house was built...