The economic life of a commercial building is not long. The hideous piece of dung now being built adjacent to your tube station (perhaps by me) may even reach the end of its economic life before you retire, its services failing, lifts stalling and repair bills soaring. One could strip such buildings back to the frame and rebuild from there - a lower-carbon option - but most of the time its easier to take the whole thing down and start again. Such is the fate of commercial buildings constructed through the 70s and 80s, and now being nubbled down to steel and rubble.
The driver of course is the P&L account and the balance sheet. Constructing to a standard that depreciates over a century rather than a quarter of that time is simply not good business. All the government's carbon targets are for cost-in-use rather than embodied carbon cost, so there's not even an economic distorter to affect the business equation.
The same doesn't hold true for monumental or grand public buildings; we're stuck with the National Gallery's Sainsbury Wing forever, however uneconomic it becomes to re-engineer and maintain. Likewise Portcullis House, and as the structure and fabric of the truly hideous Scottish Parliament building begin to fail (as I expect will start to happen sooner rather than later) we'll be called upon to stump up hundreds of millions more to keep the thing standing.
The rigour of the planning system is designed to cope not with the former but with the latter class of building; there's an inbuilt assumption of longevity that makes getting development consent even for a 'temporary' commercial building a hurdle that impacts on the competitiveness of UK business.
Now is the time to recognise the difference between the two types of development; for short-lived commercial structures, once the land is designated for this use, we should make a bonfire of development controls and free British business to rebuild its global competitiveness.