(BBC) - (Open): Vodafone started the day among the biggest risers among the FTSE 100 after results showed improvements in its major UK and German markets.

Vodafone was 2.5% higher after it reported first-quarter organic service revenue up 0.8%, faster than the 0.1% recorded in the fourth quarter.

Pearson was up another 2.7% following news of its FT sale. Despite reporting a loss, it lifted its dividend.

The FTSE 100 index was 6.57 lower at 6,648.44 points.

Shares in drinks behemoth Diageo shed 2% after the US watchdog, the SEC, said it was investigating the company over allegations it had been boosting the appearance of sales by shipping out more orders than had actually been placed.

Shares in plant hire business Ashstead dropped another 2%, putting it on course for a 12% fall over the week - its worst since 2011. It fell after investors sold out of rival hire business United Rentals following disappointing figures.

Outside the FTSE, electricity generator rental firm Aggreko plunged 15% after it issued a profits warning.

On the currency markets, the pound fell 0.23% against the dollar to $1.5479 but rose 0.12% against the euro to €1.4138.