Today I discovered a very useful feature in the latest Google Earth, (the downloaded version not the web browser one). They've started to add aerial images taken at different times, with the oldest being 1945. You can just move a slider and slip back in time. Here's a Limestone Quarry local to me shown at three different times:
http://i230.photobucket.com/albums/ee282/remoteneeded/Thrapston.jpg Note that the staion buildings are there in 1945 and 2005, but gone by 2009.
Only a relatively small part of the country is covered all the way back to 1945 but hopefully they'll add more soon. Top tip: zoom in on London, switch to 1945 view, then zoom out and you'll clearly see which bits of the country have these archive aerial shots. Also note that the alighnment of the 1945 shots isn't perfect at the moment.
You can download Google Earth here:
http://www.google.co.uk/intl/en_uk/earth/index.html Sorry if this is old news, but I've now spent all day on it and it's led to some fantastic discoveries!