There's less of a whiff of politics than you might think. The ToBA was intended to maintain an onshore ship design and build capability. That it happens to be in Scotland - specifically the Clyde - is more an accident of history than deliberate politicking. In any case, the contractual imperative to buy the OPV is partly due to the failure to order T26 - some of which is down to the inability of service staff to make decisions, rather than the CS blamestorm implied in the Times article. What is really driving this is - of course - the near years budget profile in the SDSR15 settlement, rather than any contractual failure.
This is just another round of ABC jockeying / preparation.