With the standard ceiling rose you will normally have three cables.
The feed in and out will connect like colours together however the switch cable should have two wires either red or brown according to age of wiring.
Often however a cable with line and neutral colours is used and the wire with neutral colour (Black or Blue) will have a sleeve red or Brown on it.
This wire is line not neutral and many DIY people have problems here and often due to someone losing the sleeve.
I will guess you have mixed up the cables and putting the wire which should be sleeved in with the neutrals will cause a direct short.
In the past I have tried to write guides as to how to ID each cable but I was accused of giving dangerous information and as a result so I'll leave the guiding to "Singer" to guide you through this time!
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