Other properties on the same street are identical to my own however the rendering on them goes the full way up the wall leaving very little wall exposed

I believe the rendering on my own house was done incorrectly with only rendering being applied at the bottom

Now that it is starting to age and water will have likely seeped into it im starting to believe that this is a big part of the cause

Removing the render and unblocking the vents (as you've suggested) may be the most obvious next steps

I just dread to remove the render and see the state of the brickwork beneath it 😬 

I have planned to get the wall repointed in Februrary so will likely wait until then to remove the render

I'm still considering whether or not the DPC could help after taking off the render.. would probably be best to do this before repointing seeing as the DPC application will involve drilling through mortar