Low pressure and air in hot water supply

We've got a 70's semi with a standard, vented gravity fed hot water setup.

Ever since we moved in 6 months ago, we've had low pressure in the hot water supply but more recently we've started to get a fair bit of air in the system. If I run the downstairs kitchen hot tap (mixer type) it runs for a couple of seconds then starts spluttering intermittently. The bathroom tap upstairs does the same.

Before I go doing any exploratory work, does this sound like a normal airlock problem or could it be something else?

Have you had any work done on the hot water which required turning off the gate valve on the cold feed to the bottom of the cylinder?
Check water level in the CWSC and also correct operation of ball valve.
If that's ok hold your hand over the mixer tap with a towel,turn on the hot then the cold for about 30 seconds that should force the air out.

Thanks armo. The ballcock in the cwsc (cold water storage tank I presume?) is dripping every second or so and looks fairly old. Would that make a difference?

No idea about the cylinder feed but will have a look.

Thanks, james

The level in the cold water storage cistern would make a difference to the flow rate from the hot water.
The reason I said check the ball valve was because it may not have been replenishing the water if it wasn't operating correctly.
The fact that it is dripping could indicate a worn washer which could ultimately contribute to water hammer (banging pipes).
If you haven't had any work done then the red gate valve shouldn't have been touched.
More than likely an airlock though.