Although it is probably the most likely meaning, it is not 100% clear to me that Hutton is saying that they would reduce the depletion rate of the North Sea by increasing production.  One way that it is possible to reduce the depletion rate is to drop to a lower level of production.  Isn't this the idea behind many of the peak oil 'protocols' that are out there?
Exactly.  I think the original post is a misreading of Hutton's point.  I get the feeling he's, in a sense, talking about nationalizing a resource and then controlling the production from it.  He's considering it a strategic petroleum reserve, no different from that in the US except in this case the oil has never been pumped from the ground.
I don't think Will Hutton meant to use the word "depletion" in quite the way he used it. I think he meant to use the word "production" instead.
We tend to confuse the words depletion with production decline. Once a field is being produced, it is being depleted. With production at maximum, when you arrive at a certain percentage of depletion, the production rate will start to decline. A 3% depletion rate at the start of production could happen as the field is experiencing significant year-on-year increases. When new tech is applied, you increase production, but accelerate depletion. The only way to slow depletion is to reduce production.