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