Just a thought while I was having my cup of tea: the answer to the debate over whether steel or concrete should be used for the protective barriers around the Houses of Parliament (16 July, page 15) is obvious. Sandbags – hundreds of them should suffice. After all, what was good enough to fend of the Luftwaffe in the 1940s should be good enough now. English Heritage would be unlikely to object as I’m sure they have plenty spare from historical re-enactments.