Yeah, don't have the fact to hand, but I read somewhere that the very earliest tombs are in the West of Ireland. Will dig out me books if I can remember which/where I came across it for varification.
edit 1.Navies from the off.
"Western European Origins:
The advent of radiocarbon dating has forced archaeologists to re-think the entire the chronology of western European megalithic culture. Prior to radiocarbon dating, it had been believed that megalithic culture had been brought to western Europe from the Mediterranean region, however, this was proven to be utterly false when C14 dating methods showed that the megalithic sites of western Europe substantially predated those of the Mediterranean. Not only that, but the monuments of western Europe were found to predate those of Egypt and the Near Eastern cultures also, which had previously been thought to have been the inspiration for the European megalithic builders.
The earliest dates of construction for western European megaliths are found to be in the west of Ireland. These early dates were first put forth in the late 1970's early 1980's by a group of Swedish archaeologists led by Stefan Bergh excavating in and around the Carrowmore megalithic complex. Initially, the very early carbon dates produced were met with some scepticism. The accuracy of Swedish teams findings were questioned as they seemed to shatter preconceived notions of the progression of megalith building in Europe. With time however, the megalithic sites of western Ireland have been proven to indeed be the oldest such sites in Europe.
Swedish archaeologist Goran Burenhult returned to Carrowmore from 1994 - 1998 in the hope of confirming or disproving the dates which had been put forth in the 1970's and 80's. This time however, with the aid of Accelerator Mass Spectrometry (A.M.S), more precise dates could be obtained. Radiocarbon evidence from the new excavations strongly support the findings of the previous campaign. The oldest dates from the Carrowmore complex come from Tomb no. 4. A sample taken from the foundation sockets of the stones in the cist have indicated a date of 5400 BC. Beyond this the oldest cists elsewhere in Europe are to be found at the so called Chamblandes cists of Switzerland and French Jura, giving a C14 date indicating an age range between 4800 - 3300 BC.
Just beyond Carrowmore two other sites in western Ireland have produced even earlier dates. Croaghaun in the Ox Mountains, has produced a date going back as far as 5600 BC from samples of charcoal found in the central chamber. Samples taken from a stone socket in Primrose Grange Tomb 1, have yielded a date of 6400 BC. Taken on their own, these extremely early dates for megalithic activity in Ireland are sure to draw scepticism, it should be noted by the sceptic however, that five dates from three different tombs point to activity on these sites between 6400 and 4600 BC, far earlier than anywhere else in Europe.
These very early dates prove that the practice of constructing megalithic monuments in Ireland began on the west coast. This culture thrived over the next few thousand years, with the monuments growing in complexity and reaching a peak with the awe inspiring monuments of the Boyne Valley from 3500 BC. Furthermore, these early dates prove that the megalithic culture of Ireland is the oldest in Europe, and so it should not be assumed that the culture was brought to Ireland from Britain or the European mainland, on the contrary, these findings would seem to suggest that the megalithic culture was developed in Ireland and that the practice was carried out from Ireland onto the continent. Not only is this theory supported by the radiocarbon dates being produced by archaeologists, but stepping outside the field of archaeology, a study of the evolution of archaeoastronomy and astrotheology confirm this."
edit 2
Nice Pdf here about Irish tombs.
http://www.penn.museum/documents/publications/expedition/PDFs/21-3/Nuallain.pdf
