The company said it would establish an offshore service centre in Bombay to reduce its costs.

As a result 850 jobs will go at Prudential's call centre at Reading in Berkshire.

The Prudential has double-crossed its staff and customers by making this mercenary decision

Roger Lyons Amicus

Roger Lyons, general secretary of the union Amicus, described the company's move as a "despicable act".

"The only reason being given is an 80% saving on wages, but no thought has been given to customer impact or the devastation this will cause to those affected.

"The Prudential has double-crossed its staff and customers by making this mercenary decision," he added.

Expanding in Asia

Mr Lyons said the union would campaign to reverse the decision and would be "looking at all avenues" to fight the move.

The company said it expected the changes to cost �20m by the end of 2004.

But it said it expected to make a saving of �16m a year by 2006.

Prudential will open a new call centre in India, adding to its large business in Asia.

Last week Prudential announced that it was closing its final salary scheme to new workers.