Not 100% sure I believe him - check! Council will know. Try housing department or building control.
Should have posted this before.
Property Bee. Genius. Firstly you need the firefox browser. download the property bee plug in that basically gives you extra info when you use rightmove.
It records all changes (new listing, price change, text change etc) to rightmove data BUT ONLY WHEN SOMEONE WHO USES PROPERTY BEE SEARCHES AND MAYBE EVEN CLICKS ON PROPERTY, and shows them on rightmove alongside the property. It is rather brilliant. Therefore when a property is listed property bee does not know. But when someone who uses property bee searches it does. Therefore first listed on xx date is the latest it could have come on the market - it may have been on for ages before that. If you regularly search a single area over a year you can start to really rely on the info shown!
Just downloaded this. Pretty handy.