The ex-Leicester Tigers, Nottingham, Yorkshire Carnegie and Ealing Trailfinders player, is Scotland-qualified via his Dumfries-born grandmother.
Lancaster's father is former England, Leinster and Racing 92 coach, Stuart, who represented Scotland at age group level.
The younger Lancaster played for Scotland at U18 level and has been linked with a call-up to Gregor Townsend's squad this summer for games against Maori All Blacks, Fiji and Samoa, with Blair Kinghorn and Finn Russell likely to be unavailable with the British & Irish Lions.