LONDON/VENICE, La.,  (Reuters) – Britain stuck up  for beleaguered BP Plc on Friday against American criticism  over the Gulf of Mexico oil spill, while the company ramped up  efforts to siphon more crude from its gushing well.

British Prime Minister David Cameron and his finance  minister George Osborne stressed the London-based company was  economically important to both Britain and the United States.

The British government’s backing helped boost BP shares,  which have been battered this week as the Obama administration  ratcheted up criticism of the company over the 53-day-old  spill, the worst environmental disaster in U.S. history.

Millions of gallons of oil have poured into the Gulf since  an April 20 offshore rig blast killed 11 workers and ruptured  BP’s deep-sea well. U.S. scientists on Thursday doubled their  estimate of the amount of oil flowing from the well.

BP has been capturing oil from the leaking well since  installing a containment system, or cap, last week.

It is moving a second ship to the spill site to enable it  to increase the amount of oil it is siphoning from the well  “toward the end of June,” the Obama administration’s point man  for the disaster, Admiral Thad Allen, said.

Under U.S. government direction, BP also plans to nearly  double its oil-collecting capacity by mid-July. The upgraded  oil collection system could potentially siphon up to 50,000  barrels a day, Allen said.

The well will not be sealed until August, when two relief  wells now being drilled are due to be completed.

U.S. Energy Secretary Steven Chu told Reuters that BP’s  latest effort to capture the leaking oil had not made the spill  dramatically worse, dispelling fears of government scientists  that it could increase the flow of crude by up to 20 percent.

Obama administration officials have threatened to increase  BP’s liabilities for the spill, which is causing an ecological  and economic disaster along the U.S. Gulf Coast. U.S. lawmakers  are also pressuring the company to suspend its dividend to  ensure it has enough cash to pay for cleaning up the mess.

U.S. House of Representatives Speaker Nancy Pelosi said yesterday BP should be subjected to unlimited liability costs and  should pay all damage claims before issuing the dividend.