Yes but these are factored into each price individually - therefore the UK price doesn't bear relevance to the Euro price. If you take an adults item of clothing for instance there is a 6% difference in VAT between the two prices. Should the retailer charge more in the UK purely to narrow the price differential on the dual price ticket?
But they are not quoting UK Price & Irish price on the tags they are quoting Sterling & Euro. These prices should reflect the current exchange rate. Taking that argument then there should be a list of prices in all EU countries where different rates of VAT & taxs apply.
Have just come back from Next today where an item of clothing for £30 was marked at €45 thats a 50% mark up. No external factors can justify that rip off.