By Chris Dorrell Sterling is set for its worst week all year due to changing bets on interest rates as well as the fallout from rising geopolitical tensions in the Middle East. Over the past five days, the pound has lost 1.9 per cent against the dollar and was trading around $1.311 on Friday afternoon, down from just over $1.34 at the start of the week. The decrease has knocked sterling from its remarkably strong start to the year, which has seen it outperform all other major currencies. “This week’s plunge has certainly upset sterling’s strong bull run since April,” David Morrison, senior mar…