A third arrest has been made over claims that a vulnerable man was forced to live in a 6ft shed for 40 years.
The 58-year-old was found at a residential site north of Carlisle in Cumbria - reportedly a licensed traveller camp - in a dawn raid last October by officers from the Gangmasters and Labour Abuse Authority (GLAA).
Two men aged 79 and 53 were arrested on suspicion of modern slavery offences at separate fixed residential sites north of Carlisle last October and earlier this month.
The GLAA said a third man, a 20-year-old Briton, was arrested on Wednesday in connection with its inquiries.
All three suspects have been released under investigation.
Last October, investigators found there was no heating in the cramped shed, with a soiled duvet on the floor and a metered television.
The 58-year-old has been receiving specialist support for the last six months and is living in sheltered accommodation, said the GLAA.