The Department of Justice knew there were likely to be “sensitivities” around their plan for a commemoration for the Royal Irish Constabulary (RIC) and Dublin Metropolitan Police months before the event was made public, official correspondence shows.

As controversy grew earlier this year, security fears emerged with the Office of Public Works (OPW) – which manages Dublin Castle where the event was due to take place – saying there would need to be “significant assistance” from the Garda.

“The gardaí have been in touch alright and they are very concerned,” wrote an OPW official in an email to the department on January 6th. “There have been serious protest/riot threats made.”

Documents released by the Department of Justice under the Freedom of Information Act also show just how closely involved Minister for Justice Charlie Flanagan was in helping organise the commemoration.

He even helped recommend music for the day, according to internal emails. An official wrote on December 19th “the Minister would suggest Danny Boy, some Thomas Moore pieces, and anything else which the Garda Band would deem appropriate”, according to internal emails.

The event ended up being deferred on January 7th and caused a major headache for Fine Gael in the run-up to the general election.

Emails show the department acknowledged last September that there were likely to be “some sensitivities” around the commemoration.

Members of the Black and Tans, an armed auxiliary force of the Royal Irish Constabulary, and British army privates watch fighting at the siege of the Four Courts in June 1922. Photograph: Topical Press Agency/Getty

Outlining the plan on September 6th, a department official said it was proposed that the Minister and the Garda Commissioner “could say a few words and the Minister might then present the Commissioner with a piece of crystal or something similar to mark the contribution of those who served in the RIC and DMP...

“We wouldn’t intent to do much advance publicity but would instead perhaps issue a press release that day along with a photo from the event.”

Internal records detail how controversy then started to build around January 2nd when the department began receiving negative calls and complaints on Twitter.

An internal email said: “Not entirely surprising – it’s a very sensitive area.”

Another message sent to them read: “It is… trending on Twitter and the comments are not exactly favourable! Just type in ‘Black and Tans’ in the search box and you’ll see what I mean.”

The department tried to gather information to counteract some of the “nonsense circulating” about the event.

Speaking points prepared for the Minister tried to hammer home the point that the event was not a “celebration” but one of a large number of events due to take place this decade.

Sir Hamer Greenwood, chief secretary for Ireland, inspecting the Royal Irish Constabulary (RIC)

The department was particularly annoyed about attempts to link the commemoration to the Black and Tans, internal emails show.

One message said: “This event was NOT planned as a commemoration of [them] … and it is quite ignorant of anyone to suggest otherwise.”

The department had already sent out dozens of invitations to the event, with a very large number accepted and only a very small number declined for political reasons.

After deferring the event, the department received dozens of emails saying they hoped the commemoration would take place at a later date with the majority highly sympathetic to Mr Flanagan.

The records also show how the department received more than 200 representations from members of the public and more than 20 phone calls as well. One of the phone calls was described as “very threatening”.