The Takeover Panel forced Trafalgar to retract assertions that special dividends paid by Northern aimed at persuading its shareholders to reject Trafalgar's bid would result in a commensurate fall in the company's share price.
Trafalgar admitted yesterday that there is "no empirical evidence to support the assertion".
Trafalgar House has until Friday to improve its offer should it wish to do so. Analysts believe that the cash alternative of £10.48 per share could be increased to £12.
Professor Stephen Littlechild, the director general of electricity supply, might yet refer the bid to the Monopolies and Mergers Commission.
Northern's shares closed up 8p at £11.20.