Ron Hale Marine Ltd - Zodiac Delrin Valve Diaphragm
I bought something similar here in the USA. I had to slightly drill out the center holes that the post goes thru, as they were too small.
Those scuppers are crap, as I have the same thing on my boat. It fills the boat all the way to the floor board in an hour. Have to put the regular plugs in most of the time, and if the boat takes on a lot of water, then pull the plugs and run at a good clip, before casually putting the plugs back in.
This week I plan to remove one completely and run my bilge pump outlet thru it. Mine lives on a trailer though, and can't fit inside a vehicle.