The study, which has yet to be peer reviewed, found the most common ongoing symptoms were fatigue, muscle pain, physically slowing down, poor sleep and breathlessness.
Patients also said their health-related quality of life remained substantially worse one year after hospital discharge, compared to before having Covid.
Researchers said this suggests these symptoms of long Covid are likely to be new, rather than pre-existing conditions.
The study, led by the National Institute for Health Research (NIHR) Leicester Biomedical Research Centre, also confirmed earlier research that people who were less likely to make a full recovery from Covid-19 were female, obese and required invasive mechanical ventilation (IMV) to support their breathing during their hospital stay.
Researchers from 53 institutions and 83 hospitals across the UK assessed 2,230 adults who had been hospitalised with Covid-19.
All participants completed a five-month assessment. So far, 807 people have also completed a 12-month assessment.
Recovery was measured using patient-reported data, physical performance and organ function tests.
Participant blood samples at the five-month visit were analysed for around 300 substances linked to inflammation and immunity.
Dr Nazir Lone, senior clinical lecturer in critical care at Edinburgh University, said the study highlighted the need for ongoing care for those who had been hospitalised with Covid-19.
“This is the largest study in the UK investigating the long-term impact of Covid-19 in people who were admitted to hospital and survived,” he said.
"Less than a third of survivors described themselves as fully recovered one year after discharge from hospital.
"Given that over 25,000 people have been admitted with Covid-19 to hospitals in Scotland since the beginning of the pandemic, this study highlights the need for ongoing comprehensive care for hospital survivors of Covid-19.”
Professor Chris Brightling, chief investigator for the study and professor of respiratory medicine at Leicester University, said a “sizeable population” is at risk of reduced quality of life due to lingering symptoms.
He said: “The PHOSP-COVID study is further evidence of the UK’s ability to combine expertise across both disease area and geography to rapidly gather data to help us understand the longer term implications of long Covid in hospitalised patients with persistent symptoms.
"Our findings show that people who were hospitalised and went on to develop long Covid are not getting substantially better a year after they were discharged from hospital. Many patients in our study had not fully recovered at five months and most of these reported little positive change in their health condition at one year.
“When you consider that over half a million people in the UK have been admitted to hospital as a result of Covid-19, we are talking about a sizeable population at risk of persistent ill-health and reduced quality of life.”
Dr Rachael Evans, an associate professor at Leicester University, said there was an “urgent” need for medicines and healthcare packages that target long Covid and help people return to their daily lives.