Thirty Britons were among the 38 tourists killed when a gunman opened fire in June 2015, on a beach in Sousse.

A UK tourist was also one of 22 killed in a separate attack on the Bardo museum in Tunis, earlier that year.

The so-called Islamic State claimed responsibility for both attacks.

The service will be held for survivors of the attacks and for the victims’ families. Prince Harry will also attend, and will lay a wreath on behalf of the Queen at Westminster Abbey’s memorial to innocent victims.

He will also deliver a reading during the service, which will be conducted by the Dean of Westminster.

The inquests into the Sousse killings had been due to start in November this year, but have been pushed back until next January, with judge and coroner Nicholas Loraine-Smith reportedly stating that there remained “an enormous amount of work to be done”.

Last year the government announced it would be funding a permanent memorial dedicated to the victims of the Tunisian beach massacre, as well as creating a separate site of remembrance for all British nationals killed in terrorist atrocities overseas, the Daily Mail reported.