When was the Great Britain separated from the European continent and became an island?

Until about 14,000 years ago, Great Britain was joined to Ireland, and as recently as 8,000 years ago it was joined to the continent by a strip of low marsh leading to what are now Denmark and the Netherlands. Great Britain became an island at the end of the last glacial period when sea levels rose due to the combination of melting glaciers and the subsequent isostatic rebound of the crust.