It warned that the Government's target of fully on-line government by 2005 was "not realistically achievable" and urged ministers to halt the web aspects of the programme while existing faults were rectified.
The 200-page review was commissioned by the Interactive Bureau - a website strategy and design agency - and the research carried out by Porter Research which also publishes an annual review of the FTSE-100 web sites.
It said that its findings were a "strong indication" that hundreds of Government and quasi-Government websites were in need of attention in one area or another.
The 10 Downing Street site was said to be "a mess - in need of a thorough overhaul from top to bottom".
"What is the point of the Prime Minister - the prime mover in bringing the Government to the people via the web - having a site which announces the opportunity for foreign journalists to ask him questions, yet gives no opportunity for members of the British Public to do so ?" the report complained.
It gave the website a score of just 40.75% - marginally higher than the Driver Vehicle and Licensing Agency which was rated the worst of the lot.
The Number 10 site scored so badly "because its navigation is inept, because of a lack of attention to detail, because it is poorly maintained, because the coding of it is of a low standard, because whole sections of it are inappropriately named, because of its slow speed of loading, because it does not work properly with some browsers - and because it allows no provision for members of the public to contact either the Prime Minister or his office".
In contrast, the best of the 20 sites surveyed - the Department for Education and Skills - scored 78.5%.
Quelle: IC Newcastle
