For 6mm2 T&E, I'd probably use separate 20mm oval conduits, one for each of The 2 cables, but I might guess you'd need 32mm oval conduit it you actually needed to set the two in one size. The entire thought is for me to speed up on a rewire, so https://messiahawner.aioblogs.com/81041724/everything-about-mini-trunking