By Paul Sandle

LONDON (Reuters) -European mobile group Vodafone reported another deterioration in Germany, its biggest market, in its third quarter, a weak point amid otherwise stronger trading in Britain, Turkey and Africa.

Shares in Vodafone opened down more than 6%, more than wiping out gains made in the last 12 months.

Service revenue in Germany fell 6.4% in the quarter, worse than the 6.2% drop in the second quarter, which it said was mainly due to the impact of a change in pay-TV laws and to a lesser extent increased competition in mobile.

Chief Executive Margherita Della Valle said service revenue for the group accelerated to 5.2% in the three months to the end of December, driven by a step-up in the UK and strong performances in Turkey and Africa.

"We are continuing to invest in the turnaround of our German business and we are starting to see improving customer trends, although conditions have become more challenging in the mobile market," she said on Tuesday.

Vodafone has been hit by the end of pay-TV bulk contracts in apartment blocks in Germany, which came into full effect in July 2024. It has lost just over half of its customers affected by the law change, leaving it with 4.1 million households by end-December.

In Britain, where Vodafone's merger with rival Three will complete in the coming months, service revenue grew by 7.6%, helped by the addition of 37,000 mobile contract customers and 72,000 broadband customers, it said.

The company reiterated its guidance for the full year. It expects to deliver core earnings of around 11 billion euros and adjusted free cash flow of at least 2.4 billion euros for the full year.

(Reporting by Paul Sandle; editing by Sarah Young)