Fresh from a court victory in Britain, the London Metal Exchange now faces one of the biggest hurdles yet in its years-long crisis over its warehousing policy that consumers say has inflated prices: convincing US lawmakers its reforms are enough. When Britain's Court of Appeal handed a victory to the LME last week, knocking out a challenge to the reforms by Russian aluminium giant Rusal, the exchange's head of business development, Matt Chamberlain, was in Washington, a source familiar with the matter said. Chamberlain was there to plead the exchange's case with lawmakers who have been pushing for even greater change to its warehouse policy. Senator Sherrod Brown was among the people the LME visited, a spokeswoman for the senator said. The Ohio democrat has been a fierce critic of the bourse, urging US regulators to crack down on the 137-year-old exchange and threatening to write rules that would compel regulators to intensify oversight of the exchange on US turf. Brewers like MillerCoors, which uses aluminium for beer cans, have complained that the LME has not done enough over the past four years to tackle excessive stockpiling by warehouses owned by Wall Street banks. They say this has driven up prices. Now, sources say Brown is pushing for the world's oldest and biggest metals market and its warehousing network to take its most drastic step yet: cap rent that warehouse operators can charge on metal stored in their sheds, discouraging stockpiling by putting a limit on the money to be made from storing. The lawsuit had forced the LME to halt its reforms, but last week's Court of Appeal decision means it can press ahead with the plan announced last year, telling warehouses they must ship out at least as much metal as they are taking in. The so-called load-in/load-out rule is only one of many planned changes to the rulebook of the LME to help cut waiting times to 50 days at most. It also said it would study limiting rents, but experts and the LME have previously said such a measure could be deemed anti-competitive. A source close to the LME cautioned such a measure could present legal difficulties abroad. "I'd caution that without going into whether a rent cap is legally defensible, it would take the LME into uncharted territory," the source said. "For that reason, among others, it would make the LME vulnerable to challenge from those who may not find a rent cap an attractive proposition." Many market participants say the LME may have reached the limit of what it can do: it is caught between producers such as Rusal that fear rule changes could lower aluminium prices, and industrial users that have long complained prices have been propped up artificially. But US politicians, who have led the effort for change, are still holding out for even tougher oversight.