From my experience the majority of 1960s blocks I have come across; they did not have gas when the building was designed. Sometimes they run it up the outside of the building when they do decide to fit gas. However I have found in a few blocks that the gas engineers have taken advantage of a natural smoke shaft. Now being a smoke shaft it is typically 1.5m2, so for the gas engineer, it is the perfect place to retrofit the gas supply!
Obvioulsy your shaft may not be a natural smoke shaft, without seeing it, it can be difficult to tell, but there is possibly a chance it could be.
Please ensure that the cumunal lobby (or corridor) has a menas of ventilating it, which would have been by permanent vents (PVs), or AOVs may have been fitted. This is a crucial part of the design and safety of the building and you cannot have a single staircase high rise block without it. Many (cowboy) assessors miss this.