An engineering firm reckons that rebuilding the palace could make Her Majesty much greener. But why stop there?

A nefarious plot to destroy Buckingham Palace has been exposed, but it's not the work of terrorists, anarchists or extremist property developers. No, this one comes from an engineering consultancy. Before the capital goes on high alert, Atkins, a design and engineering group, weren't actually intending to carry out this plan. In a none-too-serious assessment of the building's green credentials, rather, they dropped the hint – or was it a gauntlet? – that the Queen might be better off with a new London eco-crib.

Atkins's proposal was part of a fanciful survey by Construction Manager magazine into how much it might cost to rebuild British landmarks. It concluded that you could build a new energy-efficient replica of the palace for a knock-down £320m (Stonehenge would be £815m, but it's hard to see how you could make a collection of stones any greener). Among other improvements, the report suggested replacing the palace's 760 sash windows with double-glazed replicas, and installing photovoltaic panels, ground-source heat pumps and masses of insulation. With such changes, the royal carbon footprint would be 400 tonnes of CO² lighter every year, it estimates, and the palace's £2.2m utilities bill would be slashed by 90%.

According to a bemused Palace spokesperson, there are currently no plans to raze the Queen's London home –it is a Grade I listed building (is the Queen allowed to destroy those?). The spokesperson also pointed out that the Royal family's green credentials were actually pretty decent already, thank you. In a recent (proper) energy audit, Buckingham Palace was rated a "C" (A being the highest and G the lowest) – very good for a hulking 18th-century pile. It's had a CHP (combined heat and power) unit since 1995, it uses water from a bore hole in the garden to cool the wine cellars and for some of the air conditioning, and some of the skylights are actually double-glazed. Although, that's nothing compared to Balmoral, which is powered by its own hydroelectric plant.

But more interesting than assessing the greenness of the Queen is the prospect of a new Buckingham Palace. A replica would be 10 times more expensive than the original, says Atkins, since the craftsmen and artisans required for the job are now highly-paid specialists, rather than jobbing joiners and plasterers. And that's using a concrete and steel frame and off-the-shelf materials, rather than proper stone. But why build a replica? Despite the palace's history, it's not really much of a building, architecturally, is it? Originally the home of the Duke of Buckingham, it was bought by George III in 1761. Since then, a number of architects have tried to improve it, including John Nash, Edward Blore and finally, Aston Webb, who gave it the neoclassical makeover we all know. Nikolaus Pevsner accurately described it as "a large and rather stiff country house" – surely not the right image for a forward-looking monarchy. Why not do something a bit more urban and up-to-date instead?

The obvious problem with building any state-of-the-art eco-palace, though, is the heir apparent. Given Prince Charles's views on architecture, he probably would rather build an exact replica than anything else. On the other hand, we could give it to Richard Rogers as payback for the Chelsea Barracks scheme, which was so roundly scuppered by the Prince's intervention last year. Or put it out to competition. Just think what a decent architect could do with £320m and a prime 40-acre site. But who could or should design such a residence? To the wrecking ball, citizens!