HMRC have advised Taxation that the exchange rates currently shown on the department's website for the year ending 31 March 2012 are the average for the nine-month period 1 April 2011 to 31 December 2011 (or the nearest date if the Financial Times does not publish details on the actual day).
The figures were prepared at the same time as the averages for the year ended 31 December 2011 and the spot rates for that date.
The Revenue says the 31 March 2012 average exchange rates will be available online from 9 April 2012.