Fault one — it's blocked and won't clear.
With another toilet in the property: not an emergency. Close the angle stop behind it so nobody can add to it, shut the door, and book at standard hours. You've just saved yourself an after-hours rate for the same repair.
With only one toilet: genuinely urgent, and we treat it that way. A household without a functioning toilet is a household that can't wait until Tuesday.
Either way, try a proper plunge first — a flange plunger, enough water in the bowl to cover the cup, and firm sustained strokes for thirty seconds rather than a few sharp pushes. And check whether other fixtures are slow, because that changes the answer entirely.