I personally don’t think UK is so much challenging compared to the other smaller markets. UK is covered by Keywordspy, SEMRush and several other tools, it gets difficult when it comes down to the smaller countries, particularly the non-English ones. In terms of coverage, none of these guys really disclose their country specific database size but talks about the overall database size and I would think based on the niche you are searching for your experience could be different for each of these tools. As I mentioned, I have a clear bias of SEMRush, specifically because it not just does a kick ass job in keywords competitive research but also works as a Swiss army knife with all the various features around video ads, PLA research, Backlinks and other SEO research etc.

Thanks again,

David