A fine of £75,000 handed to Thames Water for flooding the River Crane with raw sewage three years ago has been described as an insult by an environmental charity.

The company was in the dock at Isleworth Crown Court last Friday, June 27, contesting the causes of the October 2011 pollution with the Environment Agency.

The water giant accepted responsibility for the incident immediately, which saw their fine lessened from a possible £300,000 to £75,000 because of their early admission of guilt.

It also pledged £400,000 investment into the improvement of the river in 2012.

Rob Gray, chairman of charity Friends of the River Crane Environment (Force), said: "The size of the fine, given the scale of the damage done and the finding of negligence on the part of Thames Water, feels like an insult to the River Crane.

"Three years later, and following further pollution incidents, the river has still not recovered and only now are tiny fish starting to return.

"As a comparison, this fine is equivalent to about five hours' profit for the company and less money than they made during their day in court."

The incident occurred after a sluice gate at Cranford Bridge became blocked, causing a back-up of raw sewage.

Thames Water, found to be negligent by the judge, chose to direct it into the River Crane instead of risk flooding Heathrow.

Over the next 48 hours the blockage continued to threaten a flood of the airport and three major releases of sewage into the river, the last of which continued for 15 hours.

Life in the river, including an estimated 10,000 fish, was killed in the incident.

A Thames Water spokesman said: "In October 2011 we carried out a routine operation to check the condition of a large sewer.

"This meant closing a five-tonne steel gate to hold back sewage flows so that our teams could work safely.

"Quite unexpectedly the gate jammed shut, and despite round-the-clock efforts to free it, by the time this was achieved a large quantity of sewage had entered the River Crane, causing significant environmental damage.

"We very much regret this and have made a voluntary contribution of £400,000 to the Crane Valley Partnership to spend on improvements to the river.

"We have also carried out a full review of our procedures and made a number of changes to reduce the chance of anything like this happening again."

The river last flooded in October 2013 because of a damaged sludge pipe in the Cranford area.