Managers have said the low volatility seen in financial markets is not restricting their ability to boost yields by writing call options, despite lower strike prices.
The percentage of stocks borrowed by short sellers has fallen to the lowest level since before the financial crisis, as markets continue to rally.
The US' two main markets climbed to record highs on Thursday, driven by better than expected jobs data.
The FTSE 100 was higher by mid-morning despite this morning's data from the ONS revealing a greater than expected fall in the rate of CPI inflation.
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Oil prices have jumped to a nine-month high on mounting concerns turmoil in Iraq may have a negative impact on global supplies.
Market volatility has dropped to lows not seen since before the financial crisis, prompting expectations of a sharp spike, but some strategists suggest it could remain anchored for years to come.
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