This weekend it’s open house weekend, lots of government buildings are open for free.
“Londoners are given direct access to the teams that design, construct, conserve and regenerate their environment. Alongside this are special programmes, activities and publications.” http://www.openhouse.org.uk/london/home.html
Here’s London from the top of the Gherkin last year
Unfortunately I think I’ve seen most of the good stuff now, and there’s lots of queuing (lines).
This is the que/line at the bank of England last year