Hi
I have a close coupled push button toilet cistern that is now incredible slow to fill, had a look inside just drippling in water takes hours to fill. Any help would be appricated.

I'm putting up two ballcocks, (see image) Which one's yours? Tom

Left image

That's an easy replacement. You can get the part at any hardware store. I recommend changing the supply tube at the same time

So you have a FluidMaster ball cock. This is a common problem with these ballcocks. They have a small washer with a hole,(see image) in the center that swells shut in time preventing water from entering the tank.
Purchase a FluidMaster Seal#242 from your local big box store. To replace it you will have to shut the water off to the tank and take the tank lid off. Twist the top of the ballcock off counterclockwise, (see image) and pull up. Pry out the seal and replace it. Reassemble, turn the water back on and give it a flush. Better now? Regards, Tom