The group announced a new bid which values shares in the troubled recruitment company at the same price as before, 120p, but with a larger element of cash. The offer is being extended by 12 days to May 11.
The group said it would offer pounds 57.68, plus 3.925 New Carlisle shares, plus "up to pounds 32.31 in additional cash", for every 100 shares in CSG.
Industry observers privately said they believed the new offer was a roundabout way for New Carlisle to back out of the bidding.
Last week, the Takeover Panel ruled New Carlisle must proceed with its original bid. It ruled out a condition attached to the bid by New Carlisle, that the directors at the time of the offer should keep their seats on the board.
Since the original offer was made on April 1, Jeffrey Fowler, the chairman, has resigned from the group. Mr Fowler and other directors faced a vote on 4 May, called by rebel shareholders, to install three directors led by Michael Davies, chairman of National Express.
Three more of the current directors - Ronald de Young, Tim Holland-Bosworth and the acting chairman Ralph Hulbert - have signalled their readiness to resign. But they have agreed to stay on until the 4 May vote.
The new offer requires 90 per cent acceptances by shareholders. It also stipulates that the opportunity to take the higher cash alternative announced today will lapse after 4 May.
The rebel shareholders hold over 30 per cent of Corporate Services Group. Shares in the group have fallen from a peak of 261p last year to 91p in March, before New Carlisle launched its bid.