Exchange rate for tax return

I gather the tax authorities will accept the exchange rate converting £ income into Euro from the Banque de France monthly average.

I have arrived at an average for 12 months of .7853.66 which I believe is £1 = Eur 1.2733 for 2014 Hence for every £1000 = e1273 on returns due in May 2015. Anyone have any other calculations or clues?

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