Dual Flush Toilet - No markings to indicate make and model?

I have a dual flush toliet, which re-flushes once, approx 20 seconds after the initial flush. I've tried both the short flush and long flush buttons, which appear to work correctly, but in both cases there is a second flush? Have tried to take the lid off the cistern, and have tried to twist the ring on the lid which houses the 2 buttons to remove the lid, but it wont move, so not sure if this is the correct method of removal - any suggestions to both questions?

Try pushing one of the buttons down, and pull the top of the other one off. Then remove 2nd button. On some models you`ll see a plastic posi-drive screw. Try that.

Thanks Strachan, will give it a go.

Any ideas what would cause it to flush twice? It's being doing it for the last couple of months

The flush sytem on these can become dodgey over time. The round rubber seal on the bottom starts passing water by. You may be lucky and have one of the servicable ones that twists 90 degrees and pulls out. Then you can replace it without stripping the toilet. Best to replace it and see if it cures the problem. I`ve had new ones that pass!