A prisoner who was caught swapping saucy text messages with his Highgate mistress and his wife from behind bars has been jailed for an extra year.

Convicted gunman Clayton McCalman, 24, used a smuggled mobile phone to send intimate pictures to his “north of the river” lover Monica Merrin, 31, and “south of the river” wife Masai St Aubyn-Agoreyo, 25 – neither of whom knew about the other, Southwark Crown Court heard.

The illicit communications were discovered after prison officers found the phone stashed in his cell at HMP Wandsworth, alongside 1.99grams of heroin – worth up to £400 in prison – two SIM cards and a memory card.

Merrin, a medical administrator of Shepherd’s Hill, Highgate, was ordered to complete 80 hours of unpaid work at a hearing in January after admitting unauthorised transmission of an electronic image or sound from within prison.

On Monday, McCalman’s wife St Aubyn-Agoreyo, of Tasman Road, Clapham, south London, received the same sentence after admitting the same offence. Pictures of her tattooed body matched photos stored on a memory card she had hidden in her bra.

McCalman, who was jailed for 10 years in April 2012 for having a loaded pistol in Mitcham Common, south London, admitted the same charge alongside four counts of possessing prohibited items in prison, and one count of possession of heroin.

He had a year added to his sentence, while prison officer Kehinde Fajemisin, 36, of Woodley Close, Tooting, south London, was jailed for eight months after admitting misconduct in a public office for turning a blind eye to McCalman contacting his lovers.

Sentencing, Judge David Higgins called their collective behaviour “routinely deplorable and anti-social”.