I finally visited the new Tesco extra store in Naas today. I'm not sure if all Tesco extra stores are as large as this one but the Naas store had a much larger range of Lego than I've ever seen at a Tesco store. The largest set available was the fire station but unlike the other stores there was a decent range of star wars, city and some Atlantis sets. The prices vary a fair bit with the older star wars battlepacks under €11 and the newer ones over €14. The latter is more expensive than Smyths. Indeed I was surprised that Tesco was more expensive for most items. Emperor Palpatines stood out as a €96.99 item compared to €69 in Tesco.
Not the cheapest but a useful alternative for the mid-size and smaller sets.