Short answer: PALM
According to Wells's Accents of English (1982)—the very book which gave us the lexical sets like START, TRAP, PALM, and BATH—while the TRAP–BATH split is largely absent in the north of England, words like calf, half, calve, halve, rather, Slav, shan't, can't, Iraq, corral, morale, Iran, Sudan, and banana usually have PALM (p. 135). He says, "if we were considering their pronunciation in England alone, and leaving North America out of account, we should place half, can't, banana, etc. in the PALM set rather than in BATH" (p. 356). Note though that in some accents, particularly "towards the west", there is no contrast among TRAP/BATH/PALM/START to begin with (p. 354).