I have an old ceiling rose configuration and tried connecting a new chandelier 5 bulb style light but it keeps tripping the mains when I try to turn it on. The electrician I first had out said there was a fault with the new light so I got a new one. Same thing. I've put the ceiling rose configuration back and it works fine with a single bulb but not with the new light.
Your new light probably has insufficient terminals and you're connecting wires which should not be connected, causing a dead short.
You need a 4-terminal ceiling rose or connection block: live (red, or brown); neutral (black, or blue); switched live (black with red marker); and earth (bare, sleeved green-yellow).
The earths should all go in the brass terminal to the top left - I can't see where they connect at all, they must not be left unconnected and pushed up into the ceiling - and the lives should be in the middle terminal marked Loop, not in a separate terminal.