Am trying to understand how best to provide Fire and Smoke detection on the Forecourt of an unmanned Petrol Filling Station to allow for remote alarming CCTV viewing etc.

A possibility would be a video smoke and fire detection system which will also provide security video. These systems have been around for some time and are effective in warning of a fire in its early stages but will be expensive.

They are not common and most use a manual alarm station for customers to use, to cut the pumps and call the fire service including CCTV - any detection element would probably be using video detection via the CCTV.

I was on a petrol filling station owned by tesco.it had no fire alarm panel and no call points etc .it did have the emergency pumps shutdown switch etc.

How can this be correct

If the petrol filling station was small why would they need a fire alarm, a verbally warning most probably would be sufficient, I suspect your corner shop doesn't have a fire alarm. A rule of thumb would be no fire alarm give a verbal warning, manual fire alarm and then electric fire alarm, depending on how complicated the building is.

Most petrol filling stations do not have a fire alarm, there is no point.  Fire alarms are to give automatic warning that there is a fire, most (Not all) petrol station kiosks are so small if there was a fire, it would be easy to give a verbal warning as Tom suggests