The vast viewing platform, designed by HGP Architects/ Harrington Design, is being investigated by disabled-rights groups.
It falls foul of the Disability Discrimination Act because a special lift has not functioned since the tower opened in October.
This failure of the glass external lift has dogged the tower's operator Heritage Projects for months and the organisation has become increasingly angry with contractors.
A spokeswoman for the Disabled Rights Commission (DRC), which is working with local campaigner group Speak Out, said the absence of the lift 'would break the DDA'.
'It is a very real problem if disabled visitors do not get the same access that able-bodied visitors are getting,' she said.
The spokeswoman added that if the problem is not resolved then the organisation would take the owners of Spinnaker to the County Court. The sanctions open to the court include the very real possibility of shutting it down.
In a statement, it is apparent that Heritage Projects has become extremely frustrated with the lift's failure.
'We must restate that in September last year we argued that it was inappropriate to open the Tower without both lifts fully functioning; primarily due to the restriction this placed on our operational ability to handle non-ambulant visitors safely,' it has written.
'That situation was forced upon us.
'Throughout this period the health and safety of visitors has rightly been our primary concern.
'Throughout the past nine months promises that the additional lift would be fixed have been made weekly.
'At a board meeting last month the directors of our company agreed that they were not prepared to continue to accept that the current situation was 'short-term' any longer.
'We are prepared to commit extra staff and whatever expenditure we need to alleviate this current situation. As a matter of urgency we will again consult fully with the fire authorities in relation to our proposals.
'We will do all we reasonably can to further improve accessibility now that we know it is not a short-term situation,' the statement adds.