I may be very wrong, and not to defend the Labour position, or the MAD philosophy, but I thought I’d read that the modern thinking with nukes had moved away from “use ‘em or loose ‘em”, especially with submarine based capabilities, that the strategic advantage was not with first strike, especially if you’ve shot your bolt, but rather with the response. The side responding having the now larger arsenal (assuming of course it hasn’t been depleted in the first move or lost its command and control) could exert more influence/pressure and my not need to fire in the short term, and even in the long term might have the aggressor at a disadvantage having depleted its inventory.
JAS