The Post Office expects delayed deliveries in London during the Olympic period of July 27 to September 9. Affected post codes begin E, EC, N, NW, SE, SW, W and WC. In addition, the 9am/1pm Special Delivery services are being replaced by an "anytime" Special Delivery service (but still 'next day', if posted Monday to Thursday).
So, if you are in the affected area, please allow extra time for your order to reach you.
More information at: http://www.dailymail.co.uk/news/article-2145900/London-2012-Olympics-Games-cause-day-delay-parcels-cost-1-extra.html