What is causing the switch to flip?

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I've got a 10-socket surge protector plugged into a two-socket faceplate and I'm finding that when a few devices are plugged into it, I am flipping the switch on the fuse box, which is rated at 32A.

Now I know the problem is caused by the devices plugged into this socket as I can unplug them all and the problem goes away.

What I've got plugged into the 10-socket surge protector, when the switch is flipped:

• 85W Apple MacBook Pro charger (charging laptop)
• JBL Creature III speakers
• TP-LINK router
• USB hub
• WD Hard Drive

I've also got a powerline adaptor plugged into the other socket on the two-socket faceplate.

Is this enough to flip the switch. Has anyone got any ideas what I can do?

 

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Here's the thing that's tripping (it's the black one):

 

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Unplug one device at a time and test with the remaining 4, and also try all devices but without the powerline adapter.

It's the RCD tripping due to a perceived earth fault.

So it's unlikely to be to the RCD itself?

 

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Well I've tried every device one by one and it's not tripping.

Plugged them all back into the surge protector and also not tripping. I'm stumped

 

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Sorry?