As tachograph has clarified DVSA now say any rest of less than 11 hours counts as a reduced rest for a multi manned crew.
There’s nothing to stop a multi man crew working a 15+ hour day and having 11 hours off though, so it only limits the length of rest, not the length of day. With 11 hours rest it is still possible to be on duty 19 hours.
The fact you had a shift as single manned makes no difference.