The front half of the garage is too close to the new wall. My medium term solution is to move the garage wall into the building, leaving the roof intact, to create a 900 mm space between the house wall and the garage wall.
Garage modification 2
As this is just a medium term solution I’m going to rest a sole plate on the concrete floor and then move the wall onto it. There will be damp proof membrane between the floor and the sole plate. The house is crooked in relation to the garage so this wall will be built at an angle.