As far as I know these checks are done once a year.
But this year the company that is assigned to do this job by our HA started corresponding about it 2 months before its due, regularly sending engineers every week to do it although we've arranged a date like 3 weeks before its due. we had to refuse them saying we have an appointment for another date already. the company later said if we are not in on that appointment date they will cap our gas, I found that quite disturbing as we have 3 weeks more for it to expire.
Now this year we are having it done 3 weeks early, I assume next year they will start corresponding about it 2 months early again and have it done earlier again. AIBU to think its their another way of making more money out of tenants and HAs?
By the way we contacted our HA about it, they said we can change it to near our due date later with them but their threatening behaviour like to cap our gas prevents us ever calling them again.