Do MOT advisories invalidate insurance?
No, not automatically. An MOT advisory means the vehicle passed its MOT, but the tester recorded an item that was worn, deteriorating, corroded, leaking or close to becoming a defect. That is different from a vehicle failing its MOT or being driven in a dangerous condition.
However, insurance is not only about having an MOT certificate. Most policies expect the vehicle to be kept in a roadworthy condition. If a known advisory becomes a serious defect and contributes to an accident, it may create problems during a claim.
The practical answer is simple: advisories do not normally cancel insurance by themselves, but safety-related advisories should be fixed before they become illegal, dangerous or linked to an accident.