Identify this insect found indoors in Ireland with a double tail and antennae

I just wanted to say that they are not considered a pest as some comments are telling you, they are considered beneficial. From the German Wikipedia article roughly translated: "Silverfish in low numbers are harmless. In fact they are beneficial because they eat mold. High numbers of them is usually a sign of a big mold infestation."

I myself sometimes see one or two silverfishes in my bathroom and I've seen silverfishes there (mostly at night or early morning) for at least 5 years and haven't had any problems. So I wouldn't bother throwing them out if there are only a couple.

This is, I believe, a silverfish.

This is the picture from the Wikipedia article;

A silverfish (Lepisma saccharina) is a small, primitive, wingless insect in the order Zygentoma (formerly Thysanura). Its common name derives from the animal's silvery light grey colour, combined with the fish-like appearance of its movements. The scientific name (L. saccharina) indicates that the silverfish's diet consists of carbohydrates such as sugar or starches.

They’ve always appeared for me in warm and damp places like the bathroom and indeed, this is confirmed in the Wikipedia article:

They inhabit moist areas, requiring a relative humidity between 75% and 95%. In urban areas, they can be found in attics, basements, bathtubs, sinks, kitchens, old books, classrooms, and showers.