A television cable company will fund a tree survey in east London to assess the damage to root systems caused by its contractors digging trenches.

It has also promised to replace any trees that have to be felled as a direct result of the work after a pilot survey showed the company had already damaged some trees.

The investigation, to be paid for by encom Cable TV and Telecommunications, has been forced by pressure from Havering council, in whose borough the destruction has occurred.

The initial study of 90 trees showed that more than a third suffered significant damage during cable-laying.

The secondary survey is to assess the damage and find ways of avoiding any more.

Del Smith, chairman of Havering council's development and transport committee, said cabling posed a threat to trees.

'We have 18,000 highway trees in Havering and we are keen to preserve them. We have actually diverted planned road schemes here because they would have meant trees being destroyed.'

He said the two threats to a tree's survival from cabling were when its anchorage was dislodged and its sustenance cut off. 'If there is a problem with anchorage the tree can't be allowed to stay there, but if it's sustenance then we can lop it back and allow the tree to recover.'

Mr Smith met encom executives yesterday when the secondary survey was agreed. He praised the company for its help but regretted the damage .

'I think encom have done everything to compensate for the damage. It's just sad we have got to the position we have and have lost some trees.'

An encom spokeswoman said: 'While damage to trees can sometimes be unavoidable during the construction of public utility services, encom adheres at all times to strict national guidelines which ensure that tree-lined streets are handled with the utmost care. Trees damaged as a direct result of encom activity will be replaced by two new specimens.'

She added that a cost for the survey had not been drawn up, but it was likely to be expensive.

Cabling in London has mushroomed during the past year. An industry spokesman said at least 200,000 homes were connected and that figure was expected to double by the start of next year.

Residents throughout London have protested against the excavation of their streets for cable-laying, saying it seriously damages the environment and disrupts their lives.

In Bromley, a man threatened to blow up one of the telecommunications boxes at the roadside, and another sat in a hole dug by contractors and refused to move.

Cable companies are allowed to excavate roads and lay cables without permission from the local authority. They are, however, required by law to co-ordinate engineering works with each borough.