United Utilities has found itself in hot water after carrying out unauthorised work on a forest track in the Lake District.

The water company carried out maintenance of the track at Fisher Crag near Thirlmere, part of which had not been used for a quarter of a century, to prepare it for machinery to access a nearby plantation for forestry work.

A spokesman said the firm thought the work would constitute permitted development under planning rules but it has subsequently learned it did not.

Now it is expected to submit a retrospective planning application to seek approval for the work.

Steve Ratcliffe, director of sustainable development for the Lake District National Park Authority, which manages development in the park, said: "It has been brought to our attention that maintenance work has been done to a forest track in the Fisher Crag area, near Thirlmere as part of United Utilities’ forest management plan.

"We have carried out initial investigations and it is apparent that, due to a procedural error by United Utilities, the company cannot benefit from their normal permitted development rights in this instance.

"We are now working with United Utilities to ensure that this routine maintenance work is compliant and expect a retrospective planning application to be submitted."

The United Utilities spokesman said: "We’ve been carrying out some maintenance on an overgrown forest track in order to facilitate tree felling work next year on a plantation near to Fisher Crag – as outlined in our 10-year forest management plan for Thirlmere.

"The top 100 metres of the track had not been used for about 25 years and we will need to use it to allow forestry machinery access up to the plantation.

"We were under the impression that the maintenance of the track was covered by our permitted development rights and we’ve been in discussions with the Lake District National Park Authority to clarify this. In order to resolve the matter quickly we have agreed to submit a planning application retrospectively."

The company's forest management plan for the area will see more areas of mixed native woodland introduced, with existing trees thinned and new ones planted.

The spokesman added: "Our Thirlmere forest management plan is approved by the Forestry Commission and it aims to protect and improve the environment for wildlife and people.

"We’re improving the biodiversity and beauty of the valley while protecting water quality."