If your knowledge of London extends back, say, 5 years, then you might take Heritage England's comments seriously but if, like me, your memory goes back 10 or 20 or 30 years, you will know that London's historic street scene has been steadily eroded for decades.
Possibly the first time that I paid any attention to the damaging impact of unrestrained development was in the 1980's when I became aware of the opposition to the redevelopment of Little Britain, just off London Wall. At the time I seem to remember that a group of 5 and 6 storey victorian buildings were to be demolished to make way for an office block and photographer Malcolm Tremain made some images of the area as it was then. Its fair to say that Britain, at that time, was a pretty grim place but the perceived wisdom of the time was not to renovate or refurbish but to demolish and rebuild in a glossy and superficial manner with little reference to, or interest in, the past.
Now this might suggest that I agree, to some extent, with Prince Charles about the state of British architecture but I don't. Anyone who has visited Poundbury will know that Prince Charles embraces a 'theme park' view of what he thinks is British architecture, all façadism and no substance. How much better might it have been had the good Prince campaigned to protect worthy original buildings, like those in Little Britain, ensuring that, at the same time, they might be juxtaposed with contemporary architecture of the highest aesthetic and build quality. Instead, the Prince promoted facadists like Quinlan Terry who seek to perpetuate the past through their apeing of what their selective interest suggests the past looked like, ignoring what it actually was.
The Guardian article, about the threat posed to London by the wave of applications for 'tall buildings', ignores the fact that historic London has all but been erased (certainly in the the Square Mile) leaving only the street plan as a guide to the past. These new developments have nothing to do with London's heritage and everything to do with making money, which, more today than in previous decades, is the only reason to build anything. And the continually overheating London property market will ensure that this remains the case, as long as our selective inattention allows us to ignore it.