Green’s Dictionary of Slang

(UK drugs) drug dealing outside the usual metropolitan centres; the dealers — who set themselves in a borrowed flat or house up for a short period — are often young people hired for the job by adult drug wholesalers.

2016		1011 ‘Next Up?’ 🎵 OT, I don't like doing deals like Louie.
2019		Headie One ‘Ball in Peace 🎵 I'm either OT dealing with the drug squad or in the hood, it's armed police.
2021		Central Cee ‘Sex Money Drugs’ 🎵 I’m gettin’ DMs from youts sayin’ that he wants P, can he go OT?