The 29-year-old has gone missing from hospital after being taken there for treatment from Ford Prison.
Meechan is currently serving a sentence of seven years and six months in prison after he was convicted of conspiracy to rob in Croydon.
He was taken to St Richard’s Hospital in Chichester for treatment after injuring his foot in prison but while being treated he escaped from a guard at about 1pm today (Thursday 9 July).
Meechan is white, six foot and muscular. He was wearing a white t-shirt, grey shorts and green Nike trainers and had a limp when he escaped.
Inspector Rob Moore said: “We need to get Meechan back into custody as soon as possible so I would urge anyone who has any idea where he could be to contact us.
“He has links to Surrey and London but could still be in Sussex so I would urge everyone to keep an eye out for him.
“If you think you have seen him, call 999 but do not approach him.”
Anyone with information should email email@example.com quoting serial 711 of 09/07, call 101 or contact the independent charity Crimestoppers anonymously on 0800 555111.