According to Mr Shields, waiting lists for mental health wards are growing because NHS trusts don't have the funding to get people through the doors.
He said: 'The funding of mental health services has never kept pace with the demand for it, and has been secondary in many ways to other NHS services.
'We need to be given the money we need, in order that we can have adequate staffing and resources.
'There are seriously ill people who cannot get into mental health wards simply because there aren't any more beds to go around. That is unacceptable to me.'
Mr Shields added that the ideal place to provide care is in people's homes, but that there can come a time when 24/7 support is required.
The news comes following a Care Quality Commission (CQC) report into the trust’s acute mental health services in February, which concluded that Southern Health ‘requires improvement’.
The chief executive admitted that this was the case, and has submitted an action plan to the CQC in response to their concerns.
But he believes that part of this improvement could be sparked by better funding - which could also take some of the pressure off other services.
Mr Shields said: 'The issue for me is the balance between mental health and physical health funding. I am extremely passionate about mental health services but don't believe we should be separated from physical illness.
‘People who suffer from long-term mental health conditions have worse physical health, and deteriorating physical conditions impact people's mental health.
‘In the last year there has been quite a significant rise in the investment into mental health and that has been a positive improvement, but there is still so much more we could be doing.
‘That can only happen if we have staff coming through the system and more resources to use.’