A judge has approved a legal request by a group of former Enron workers to hire lawyers to investigate bonuses that were paid to executives and traders shortly before the energy giant's spectacular collapse in December last year.

Having given up the right to sue for more severance pay after accepting individual sums of up to $13,500 (�8,550), the workers are now targeting bonuses paid to prevent executives from leaving the firm.

Retention bonuses of more than $100m was paid to about 600 Enron employees in November last year.

Just over half the money went to 500 senior employees with the rest being shared out between 756 traders.

A few days later, Enron laid off 4,500 workers.

These employees were initially offered just $4,500 in severance pay, though they received an additional $1,100 soon thereafter.

Under their original Enron contracts they should have received substantially more.