Almost a dozen Solent Trust patients were forced to travel more than 60 miles to receive mental health treatment due to a lack of beds, new figures show.
It comes despite a government pledge to end inappropriate out-of-area mental health placements by March 2021.
These placements are defined as a patient admitted for treatment at a facility outside of their usual network of mental health services because there are no local beds available.
Mental health charity Mind said the Government "must do far better" for patients with mental health problems.
NHS England figures show Solent NHS Trust forced around 10 mental health patients to travel more than 60 miles to receive treatment in the year to October.
In total, approximately 15 patients were sent away for out-of-area placements because there were no available beds.
Figures are rounded to the nearest five.
Across England, 785 patients were inappropriately being seen out of their area as of the end of October – up from 685 the year before, and the highest figure for any month since March 2019.
But none of these were at the Solent Trust.
Gemma Byrne, policy and campaigns manager at Mind, said people being forced to travel to receive treatment is costly for the NHS and can worsen patients' mental health.
Ms Byrne added: "We urgently need to see investment in mental health services reaching the frontline. The UK Government has rightly made ambitious commitments to improving mental health care, and the need to deliver on these promises cannot be overstated.
"It must do far better for the people with mental health problems in its care right now."
Health think tank Nuffield Trust said out-of-area placements indicate a "whole mental health system under pressure".
Acting director of research Sarah Scobie said: "A lack of focus on prevention, delays in patients leaving hospital, increasing pressures in community care and a lack of crisis response can all increase the pressure on bed capacity, which can in turn lead to reliance on these unacceptable out-of-area placements."
Analysis by the Financial Times showed NHS trusts paid more than ever for out-of-area mental health placements in October.
The figures show trusts spent £14.5 million on inappropriate appointments.
An NHS spokesperson said while mental health services are being expanded, they are "under significant pressure", with community crisis services seeing a 30% increase in referrals since before the coronavirus pandemic.
A Department of Health and Social Care spokesperson said: "Everyone should have access to safe mental health care close to home, and we remain committed to ending inappropriate out-of-area placements for adult patients."
The DHSC said an extra £2.3 billion per year will be invested in mental health services by March 2024 so an additional 2 million people can receive support, with an added £150 million to help those in crisis.