Use the following formula to determine if an arbitrage opportunity exists and which currency to borrow.
if 1 + rD > [(1 + rF)(Forward rate)] / Spot rate then borrow foreign.
1.0723 > [(1.0694)(1.70)] / 1.73
1.0723 > 1.81798 / 1.73
1.0723 > 1.0509, therefore borrow foreign (pounds).
Alternatively, the dollar is appreciating. [(1.73 ? 1.70) / 1.70] = 1.76% and the $U.S. interest rate is higher. Clearly, investing in $U.S. (and borrowing pounds) is the way to go.