For decades after the deal, Australians would continue to sing the U.K.'s national anthem and refer to their currency as the Australian pound.

WSJ: Australia Lawmakers Seek Split From U.K. Monarchy

The index measures the dollar against a basket of other major currencies, including the euro, yen, U.K. pound, Australian dollar, Canadian dollar, Swiss franc and Swedish krona.

WSJ: WSJ, FX Trader Launch Dollar Index

Both the pound and the Australian dollar have weakened considerably against the euro since July.

BBC: Paddy Power has 'strong year' in 2012

Pressure to buy yen can be seen in the sharply higher volatility, spiking up to 9% from 6% earlier this month, according to Interactive Brokers, which notes that there is also higher volatility in the Swiss franc, another carry-trade currency that is rallying this week against the British pound, the Australian and Canadian dollars and the euro.

FORBES: Carried Away

The firm already is betting that the pound will fall against the Australian and New Zealand dollars, reflecting the firm's downbeat view on the U.K. economy, and he wouldn't necessarily increase the negative view on sterling if a downgrade materialized.

WSJ: Sterling Braces for a U.K. Credit Downgrade

The Lonely Planet suffered from the prolonged global recession and the Australian dollar appreciating to 58% against the UK pound - 80% of Lonely Planet's revenues are generated from foreign currency.

BBC: Worldwide sells Lonely Planet business at ?80m loss