Sorry to hear that, but it happens.  There is the urban legend of slipped liners/porous block but TBH I'd just do the head gasket, look at the liners whilst it's apart though.
The gaskets will set you back about £50 but I'd strongly advise having the heads skimmed and lapping the valves in.  Use composite head gaskets which are thicker but more reliable.  Essential if you have the heads skimmed.