If you take for example UK and check one keyword in ad word Google and Keyword tracker uou will get diffient number of search with significan diffirence. Why this?
Are you referring to the Free Wordtracker tool? I wouldn't trust that tool 100% and would recommend G Adwords over it. It's hit and miss with WT. When I first started, I used WT and thought I had great KW's to target based on the search results but soon realized that the numbers were completely off when I reached #1 in G and got 1-2 hits/day. The G avg volume is more in line with what people are searching for in my opinion. Hope that helps!
Wordtracker doesn't appear to use Google's data, using instead their own selection of minority search engines. The problem is that their data sources are not representative of Google, which has nearly 80% market share. Indeed many of my bigger clients sites that receive tens of thousands of visitors per day tend to get over 90% of all of their traffic from Google. As such, there's little point using Wordtracker now that Google is disclosing actual search volume numbers.
The Google tool is the best tool to use because it bases its data on actual figures. Wordtracker uses Metacrawler search engines etc which account for around 2% of SE traffic. Everyone should use the Google adwords tool going forwards as Google is the most important search engine. Realise that all other keyword tools are insignificant in comparison to the Google tool. From my experience if you do your research using the Google adwords tool and have a solid concept and affiliate/adsense campaign etc then you will succeed.