What could cause a fuse to trip?

It’s generally the kettle or the toaster.
Best way to find out is to unplug everything from the circuit and then go round connecting and unconnected everything individually until you find the culprit.
The last time this happened to us it was the oven. The fan had become stuck and after a few minutes it blew the trip. It’s a high voltage item so it blew both its own fuse and the main fused.
Our other regular offender is the Dualit toaster. it always happens after Hot cross bun season. The fruit gets stuck in the heating element and shorts the current (😂).
The first time it happened I thought that the toaster was done for but after reading the instructions to see if I could have it repaired I just cleaned it out and it’s been fine.

Kettles are another common cause along with steam irons. We have had the odd light bulb do it and until you test them all you can’t tell.

If when you switch everything off and disconnect but the trip still goes then you need an electrician. Mice and rats can cause short circuits if they have chewed through cables and electrocuted themselves.
Water leaks inside walls are another cause.

Hopefully it’s just a toaster full of crumbs or a dead kettle.

Faulty appliance or an overloaded circuit. Is it an old house? You can get an electrician to tell you what are on which circuits and therefore what’s likely to overload. Splitting the circuit is possible.

Could be many reasons. Faulty light bulb, kettle, toaster, anything that came on at the exact moment the fuse tripped.