Dripping toilet where do I start?

[BathDIY]

Toilet constantly dripping and refilling.

Have looked at a couple of videos but can't seem to see a system that matches what I have.

What should I be looking to replace am a complete novice when it comes to this type of job.

Hoping it's a simple buy this and replace it.

 

[oldbuffer]

1. If the water in the cistern never reaches the overflow level (the big hole in the centre of the white plastic flush valve, in the middle of the cistern), then it is the seal at the base of the flush valve.
2. The flush valve is usually fixed on a sort of bayonet fitting. Water off, push down slightly and turn 1/8 to 1/4 turn anticlockwise.
3. There will be a rubber seal on the base. Try cleaning this seal and its seating in the cistern, replace and retry. You might be able to take the seal off and reverse it.
4. If 3. doesn't work, try and identify the make / model of flush valve and get a new seal. Have a look at toiletspares.

 

[CBW]

Looks like a Siamp storm? http://www.siamp.co.uk/storm-33a/