Deterrence in the Bomber-Delivery Era

Were the British and French nuclear arsenals too small to matter beside the Soviet force?

No. Because all sides still relied on bombers, interception and the chance of penetration mattered as much as raw arsenal size.

The smaller British and French nuclear forces could still matter. In 1956 every power depended on bombers to deliver nuclear weapons rather than on mature ballistic-missile forces. Radar and sufficiently fast fighters could intercept those aircraft, so delivery was uncertain in a way later missile warfare would not be. Deterrence depended on whether some bombers could penetrate as well as on the total number of weapons.