Shares in Royal Mail have dived after it warned that the company's transformation programme is "behind schedule", despite improving profits and revenues over the past six months.

The delivery giant's shares slid 16.7% to 192.4p in early trading after it also cautioned investors that its UK business could make a loss in the next financial year.

It also fired a warning shot to unions over the continued threat of strike action, saying industrial action "can only hurt" the company.

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The firm updated investors over the performance of the business just a week after it secured an injunction to block postal workers from taking part in strike action.

In the trading update, the London-listed company warned that the UK division could be loss-making in the 2020-2021 financial year, due to revenue and cost headwinds as well as significant investment by the company.

However, Royal Mail hailed its best UK sales performance for the "past five years" but warned the outlook for its letters business is "challenging".

The delivery giant saw revenues rise 5.1% to £5.16 billion in the half year to September 29.

It jumped to a £173 million pre-tax profit, up from a £33 million profit for the same period in 2018.

British Gas owner Centrica has revealed it lost another 107,000 household energy accounts in the four months to October as it also upped its annual cost savings by £50 million.

The UK's biggest gas and electricity supplier said it had eased the rate of customer losses, which was lower than the first half of the year.

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The group also said it now expects annual cost savings of £300 million from the previous target of £250 million, while it is trimming planned investment spend by £100 million to about £800 million.

Centrica confirmed it expects full-year results to be skewed towards the second half of the year, with the result dependent on weather and wholesale energy prices.

Centrica said while UK household supply accounts fell, this was offset by stronger demand for services and homes solutions, leaving total consumer accounts 136,000 higher in the four months to October.

Outgoing chief executive Iain Conn, who recently announced plans to step down next year, said: "Our performance has been solid so far in the second half of the year and we remain on track to achieve our full-year targets.

"I am encouraged by further growth in customer accounts and the recovery of business energy supply margins in North America, while we also continue to drive material levels of efficiency and maintain capital discipline."

Centrica shares lifted 6% in early trading.

Naked Wines founder Rowan Gormley has announced plans to step down as the group enters a "next chapter" following the sale of Majestic Wine to become an online-only retailer.

Mr Gormley - who set up Naked Wines in 2008 and headed the combined group following its merger with Majestic in 2015 - will hand over the reins after the busy festive season to chief operating officer Nick Devlin.

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Shares in the group dropped nearly 3% on news of Mr Gormley's shock departure and as it revealed widening half-year losses amid tough trading in the UK and Australia.

Mr Gormley said the time was right to stand down as Naked Wines moves into the "next chapter of growth", setting its sights on the US market.

It comes ahead of a major strategic switch for the group, which has rebranded as Naked Wines after its fast-growing online business.

It is soon to complete the sale of its under-pressure retail business Majestic to US firm Fortress Investment Group for up to £111 million, leaving it as a pure online wine seller.