Had this problem before and it ran for almost a year before we figured it out. Sockets on the one fuse would trip. They could not be untripped until hours later. So some phenomenon was appearing for a few hours at a time, then disappearing.
Turned out to be water, leaking through a crack behind the sink, making wires to a kitchen socket damp. After a few hours the wires dried out and the electricity could go on again. Copped it one day when during a particularly vigorous washing up bout the power went. The obviousness of it (solutions always seem obvious once you find them) drove us demented.
So check for water sources, damp leaking behind sinks, baths, immersion or whatever. The tiniest amount of moisture near electricity wires will temporarily trip the supply, and the problem will right itself when things dry out..
But if you don't find out fast, get an electrician. Dodgy things happening with electricity at home aren't to be treated lightly. Though two electricians came and went without copping it in our case......