(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.

Thames Water customers face the prospect of a £230 jump in their annual bills to help secure its future, after a potential rescue deal collapsed.

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.