(Reuters) -U.S. investment firms Silver Point Capital and Elliott Management are formulating a 10-billion-pound-plus ($13.53 billion) rescue package for Britain's Thames Water, Bloomberg News reported on Friday, citing people familiar with the matter.

The water company said the decision not to proceed with the equity raise created uncertainty around its plan to stay afloat, raising the prospect of nationalization.

Thames Water is running out of options for the equity funding it desperately needs after preferred bidder KKR & Co. pulled out of a rescue deal.