===Principle of quoting exchange rate on an arbitrary date=== 
 IMO, it is not a good idea in principle to quote exchange rates as at some arbitrary date.  It is not sustainable and not encylopedic.  An annual average is far more useful.   
 * It is not sustainable because it is unrealistic to expect that it will be revised for all currencies every day.  Anyone who needs to know the actual daily rate will use a reliable source like XE.COM or OANDA.COM 
 * It is not encyclopedic because, by capturing the rate on an arbitrary date, no useful understanding of long term price is conveyed to the reader.  
 
 The historical exchange rates (since 1990) that are given in Exchange rates section of the Economy of the United Kingdom entry. are far more useful. Spikes are smoothed and the reader gets a far better idea of the relative prices and how they move over time. It only needs to be updated once a year and the exact date is not critical.