As nouns the difference between pikey and scally
is that
pikey is a low-ranking soldier who merely carries a pike or
pikey can be (british|pejorative) a working-class (often underclass) person; can vary from specifically irish travellers to gypsies or travellers from any ethnic background, but now increasingly used for any socially undesirable person, with negative connotations of benefit fraud, theft, single-parent families and living on run-down estates while
scally is (pejorative) a rascal or miscreant, a scallywag.
As a verb pikey
is (uk|slang|derogatory) to steal.