The controversial proposed state visit by Queen Elizabeth II is set to cost the taxpayer in excess of €8m in security costs, and groups are already planning protests against the historic trip.

Gardaí will erect a ring of steel for the queen's visit – which is likely to take place next year – in anticipation of threats from the likes of dissident republicans and Islamic extremists to the safety of the head of the British monarchy.

Tom Clonan, a retired army officer and military expert, said that such a visit would have the same costs attached as any of those by US presidents – George Bush Jnr's visit alone cost in excess of €8m.

Negative public reaction began to mount immediately after Brian Cowen's comments last week that an official visit could be arranged before the end of 2011.

Speaking to the Sunday Tribune, Clonan said there was a "clear and present danger" to the British head of state in Ireland, both from dissident republicans and Islamic extremists, that could not be underestimated.

"For Clinton and especially for Bush, the greatest threat that would have been identified would have been
Islamic extremists," he said. "For the queen you have a range of concerns, but the major one, the clear and present danger for the queen, is dissident republicans, and they are active.

"For that reason all the security that would have been in place for the US presidential visits would be in place for this. The security for the queen would be the equivalent of the visits of prime ministers before the ceasefire."

President George Bush Jnr's 18-hour visit to Dromoland Castle, Co Clare, in June 2004 cost the state €4m in garda overtime alone, while the full bill for security precautions came in at over twice that figure.

A visit by Queen Elizabeth would involve significant garda manpower, as well as army and possibly Air Corps support.

Every area the queen will visit will have to be sweeped in advance for security purposes, which will pose a logistical nightmare, and thousands of gardaí will be on duty while she is on Irish soil.

News of a possible visit by the British monarch provoked an immediate backlash from the public and certain political quarters.

Not surprisingly, the republican socialist party Éirigí was straight out of the blocks, criticising the plans and vowing to oppose the visit with demonstrations.

"In the aftermath of the publication of the Saville report, the extensions of an invitation to Windsor would be a massive insult to the victims of British state violence across Ireland," it said in a statement.

Blogs and online forums were also quick to adopt the subject for public debate.

One contributor noted: "Personally I am opposed to this. The idea of monarchy and one person just as a result of genealogy and primogeniture being a ruler of a country is sickening to me as a democrat. I'd feel the same if it was the Dutch queen or any other hereditary ruler."

Others were more supportive, with one in particular commenting: "They should at least get the same welcome as they extended to our head of state, which as I recall last time was pretty good and included tea, biscuits and probably crumpets.."