A cross-party group of ministers on the Transport Select Committee said on Monday that it recognised congestion charging would create difficulties for businesses relying on vehicles in charging zones wherever it is launched throughout the country.
Focusing on London, it revealed fears that the already creaking public transport system would be unable to cope with the number of additional users who might give up their cars when the £5 charge is introduced on Monday.
Ministers added: 'It is unrealistic to expect a large number of car commuters to switch to buses, particularly when they are travelling long distances. They are more likely to switch to rail services, which are already crowded to bursting point.'
Despite this, London Mayor Ken Livingstone plans to spend the bulk of his first year's takings on upgrading the bus network.
The Select Committee report continued: 'We recognise the charge is going to cause difficulties for vehicle-based businesses. Large businesses may be able to absorb the charge within their costs, small businesses may not.'
Even moving to alternative fuels may not help, as a 100% discount for the cleanest alternative fuel vehicles may be scrapped if congestion is not reduced in the short-term. MPs said any such move would damage the scheme's credibility.
The report called for electronic charging scheme technologies to be developed to a national standard, with is compatible with any future European standard. They must also be compatible with tolling schemes elsewhere in the UK, such as the new M6 relief road toll.
MPs also attacked the Government for its lack of leadership, saying: 'The Government is committed to addressing these issues on a national level. We therefore find it a matter of serious concern that the Government is not at present prepared to make a more positive and open contribution to the national debate on congestion charging.
'Its policy towards charging schemes is now drifting and its approach to urban charging risks being fudged.'
The MPs' comments come as fleet suppliers gear up to help fleets cope with the launch of the charge in London.
Among them is LPG supplier Calor, which has a fleet of 50 Calor-branded motorcycles on the road reminding drivers that the cleanest alternative fuels can escape the charge.
The company cautions fleet operators against assuming that converting to LPG will automatically beat the congestion charge only the cleanest conversions receive a 100% discount.
Nevertheless, it believes that the new regime will underline the environmental and cost advantages offered by the fuel. Companies including the RAC, AA and Alphabet have also launched guides to help fleets through the problems they face in coping with the charge.
The RAC is offering information about congestion charging to users of its 1740 mobile phone service. Motorists dialling the service can download a step-by-step guide on how the charge works and where to pay.