Firstly you probably have some leakage current issues - there's no base-emitter resistor
for the BC557 so it will amplify the leakage current of the BC547 when its off, and this will
create a small voltage across R29, which might be problematic.
Add 1k between base/emitter of the BC557, reduce R29 to 1k or so to reduce this effect -
though that might not be the issue.
You need decoupling on all your supply rails really. If there are spikes induced on the
12V rail they can sail straight through to the FET's gate. Adding a 15V zener as protection
across the gate/source of the FET might be a wise precaution.
Your circuit is unconventional using an emitter-follower for the level converter NPN
stage - here its not a problem as the current is low and its not going to overheat,
but if you were switching more current it could be an issue.
Your fuses need to be on the incoming supply rails and not to ground - one of the scenarios
fuses protect against is shorts to ground - a fuse to ground cannot protect from this, your
supply wiring is thus not protected from overload/fire.
You didn't say what the load actually is - the IRF540N has an on-resistance of 52 milliohms
so at 10A it will dissipate 5W, which will fry it without a mid-to-large heatsink.
[ In electronics / engineering use numbers and units, not adjectives, "high load" could mean radically
different things to different people ]