Pixiq reported today that Nikon UK increased the price of the Nikon D4 by £500 and the D800 by £200, with immediate effect. The information is based on an email sent from a Nikon UK general manager. The previous pricing was described as a "systems error".
Few days ago, the price of the D800 dropped £300 for few hours on Amazon UK.
I emailed few sources in the UK but could not get a confirmation for this price increase (probably because of the time difference).