ukWaC is a 2 billion word corpus constructed from the Web limiting the crawl to the .uk domain and using medium-frequency words from the BNC as seeds. The corpus was POS-tagged and lemmatized with the TreeTagger. The tagset is available here, more information can be found in this paper.1)
M. Baroni, S. Bernardini, A. Ferraresi and E. Zanchetta. 2009. The WaCky Wide Web: A Collection of Very Large Linguistically Processed Web-Crawled Corpora. Language Resources and Evaluation 43(3): 209–226. (PDF to download)