Just a matter of political will and money. Remember much of the Tube Alloys work happened in Canada, and the Canada natural uranium/heavy water reactors are great for breeding Plutonium.
Given an early decision for it we'd have the bomb sometime after Britain ('52), but before France ('60).
Of course, why would we want to?
In the 70's we could likely have had a bomb in like 6 months from the go ahead, or less.