Based on a more conservative 800m valuation for the carrier, the proposed offer to pay 104m into the staff pension scheme could be knocked off any value put on the airline. Aer Lingus management has tabled the 104m top-up as part of a package of sweeteners including lump sum payments of up to 4,000 to each of the 3,600 employees in the hope of easing through the planned autumn flotation.

One UK analyst told the Sunday Tribune last week that the carrots being put in front of staff and unions, which include a 3% pay increase on top of the national agreement, are "likely to be an extra drag on earnings potential".

One source in Dublin said any money being paid into the pension will have to come from cash and will directly affect the airline's valuation.

He said potential investors would be likely to seek assurances that the sweeteners will be awarded on the basis that unions will not attempt to interfere with the future development of the business.

Should such promises be forthcoming, that could make the flotation an appealing investment. Staff are also being offered up to 7.5% of future profits to buy shares in Aer Lingus.

However, should a downturn occur in the industry, the assurances being offered would weigh heavily on the airline's finances.