Britain's alliance risks in the Vietnam counterfactual

Would the British Empire be better off letting the two sides continue fighting in Vietnam?

In that counterfactual, it could choose this cruel option to preserve the US alliance, avoid war with the Soviet Union, and gain freedom of action elsewhere.

Trying to force an end to the conflict could risk Britain's American alliance. Confronting the Soviet Union directly would bring a different danger of war. Letting both powers spend resources in Vietnam could instead leave Britain with more influence elsewhere and across the Commonwealth. The harm to the Vietnamese people makes this calculation cruel despite its strategic attraction.