Cracks on internal walls - Victorian Semi-Detached

[crackpeter1903]

Hi!

We recently purchased a Victorian semi-detached in London, built on what I believe is very clay-like soil.

Whilst removing some blown plaster in one of the front rooms, we uncovered a pair of cracks like in the photos attached, either side of the hallway. What should our remediation options be? Simply filling with a lime based mortar? Installing some form of ties? Eg helibars?

Cracks are wider at the top than the bottom, but seem to be historic; ie quite dusty in general. There are some bushes near the front of the house which I will be removing, and a large eucalyptus towards the back that the neighbour says will be removed.

 

[crackpeter1903]

Here’s a picture of the crack in the other room.

One thing that’s suspicious to me is that the dwarf wall underneath both of these sections has been removed somewhat substantially in the past in order to run services (plumbing, electrics). Possibly shoring this up would also be advised?