The 250V is the limit where the fuse will not arc across itself (ie voltage over 250 V could get by a blown fuse)
Current is current.... a fuse will blow at its amp rating regardless of how much voltage is involved.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)