Ray Cole, from Deal in Kent, was arrested by police in the Muslim country for "homosexual acts" and was last week imprisoned for four months, his son claimed.
The family of the 70-year-old, who came out as gay a few years ago, have launched an internet campaign to demand his release and a number of politicians have urged the Moroccan authorities to act.
His son, Adrian Cole, said his father has been condemned to a "bleak" and overcrowded prison where he is forced to sleep on a concrete floor.
In a post on his Facebook page, he wrote: "Many of you who know me will know that my father came out as gay a few years ago. He had been holidaying in Morocco with a Moroccan friend and sadly has been arrested and charged with being gay.
"He has now been sentenced to four months in the central prison in Marrakech. Life is pretty bleak in there, they are served boiled vegetables once a day and his cell is a dorm designed to sleep 44, however since there are 60 men in there, my 70-year-old father sleeps on the concrete floor.
"The prison does not segregate, so he is sharing with murderers, rapists, paedophiles etc. We have been working with the foreign and common wealth office, but of course they cannot change the law.
"What we can do though is make this an embarrassment for the Moroccan authorities, this country produces nothing, they rely on tourists, like my father. They then decide to judge you and your life and may or may not treat you in this fashion."
It is understood that when Cole was arrested police searched his phone and found photographs which they used to prosecute him in court.
Charlie Elphicke, Conservative MP for Dover, branded the charges "medieval" and said it showed British tourists are not safe in Morocco.
He said: "I have been doing all I can to help free Mr Cole from these appalling charges. I am deeply concerned about his safety and it is clear that if you visit Morocco you are at serious risk of facing trumped up charges for medieval crimes.
"The message is clear - Morocco is not safe for British tourists.
"I am gravely concerned by the state of Moroccan prisons, and the care and the safety he will have in jail.
"I'm raising it with ministers, asking them to intervene more directly on his behalf. It is a shocking and appalling situation for a British national to be in, and it is really important to get him back to the UK."
A #freeraycole hashtag has been set up on Twitter and a Facebook page has also been set up calling for Mr Cole's release.
A Foreign and Commonwealth Office spokeswoman said: "We can confirm the detention of a British national in Morocco. We are providing consular assistance."
The Foreign Office website states that homosexuality is a criminal offence in Morocco. It states: "Sexual relations outside marriage are also punishable by law."
Former deputy speaker of the House of Commons Nigel Evans lashed out at the "archaic" law that has sent Cole to prison.
The Conservative MP for Ribble Valley called on Morocco to release Cole, a retired magazine publisher who was imprisoned last Thursday alongside Mr Jam Wald Nass.
Evans, a gay MP, told PinkNews: "I am astounded that Ray Cole has been convicted of homosexual acts.
"I have been to Morocco on a few occasions and I find it a lovely, and vibrant country. Morocco attracts thousands of UK visitors every year and a fair whack of them will be gay.
"I deplore the fact that Mr Cole is spending any time in a jail there. I call upon MPs from Morocco to look again at the way they are treating gay people.
"Do they really want their country associated with such archaic laws, and do they really think it is wise to lock someone up for four months for something that is legal in so many countries around the world?
"As a gay MP who sits with so many other gay MPs in the UK I will be writing to the Moroccan ambassador and asking her to convey to His Majesty a plea from the gay community in the UK to release this man in order that he can return to the UK as soon as possible."Suggest a correction