The planning application design and access statement talks about extension but the drawings suggest that they would not knock through the wall and would only add two employees in the expanded space. It seems odd to run an estate agent in two disconnected properties with two front doors (and the final employee density would seem luxurious by many standards).

This still looks like a move to me, not an extension. They would be under no obligation to retain their current property (nor should they be).

I don't object to either a move or an extension in principle but hope that SR will do the right thing and be completely transparent about their intentions and clarify their application & drawings.

Or perhaps it's Cantel who need to do the clarification. The root cause of the problem on the parade in recent history has been mostly about landlords, not tenants.