Dr Martens is to step up the price of its boots by 6%, as it says the cost of labour, energy and supplies, including the bouncy soles and leather, has risen. The Northamptonshire-based footwear group will increase prices for the second year in a row on the classic boot, which currently costs about £159, adding £10 to the price. The rise will come next autumn to reflect higher production costs that the company has now locked in over the course of next year. Announcing its half-year results, Dr Martens revealed a disappointing 5% fall in pretax profits in the six months to 30 September despite a 13% rise in sales, as the company said it had invested more in marketing, staff and new stores. The firm said about £10m of sales expected during the period were delayed because of strikes at the port in Felixstowe and staff shortages at its distribution centre in the Netherlands. Kenny Wilson, the chief executive of Dr Martens, said he was “very confident about our outlook for Christmas”. He said the group was still seeing inflation in the cost of supplies “across the board”, from the oil-based product used to make its soles, to leather and energy. “We will only put prices up to cover inflation. This year we put prices up for the first time in two years and will cover inflation next year,” Wilson added. Staff costs are rising, and Dr Martens is offering a £500 cost of living bonus – paid out over October and November – to about 2,000 of its 3,500 workers around the world. The payment will go to staff who work at least 20 hours a week and earn less than the equivalent of £45,000 a year – from the UK factory and head office to buying teams in the US, Europe, South Korea and Bangladesh. Wilson said the company was making the payment as its workers were facing “very tough levels of inflation” around the world: “At the end of the day, people are the differentiator. We have a highly engaged workforce and wanted to show we cared for people who work for Dr Martens, and actions speak louder than words.” Shares dived almost 24% as the company warned of “variable trading” in recent weeks, partly because of mild autumn weather in the UK and Europe, and said that profit margins would take a hit. John Stevenson, a retail analyst at the brokers Peel Hunt, said the figures indicated “some worry for apparel stocks into peak trading, reflecting those higher stock levels and adverse weather patterns”.