Thanks to robust search tools like Google, this question can easily be answered in a few keystrokes. When "#1 song in the UK now" is searched, the first organic link listed is fellow search engine competitor Yahoo! It reports DJ Fresh and Sian Evans' song "Louder" is in its first week at the top.
However, The Top 40 charts is the next organic link listed which argues Jason Derulo still holds the title with "Don't Wanna Go Home" for the second week in a row.
"Now That's What I Call Music!" managed to find its way to the top spot on both Yahoo! and Bing instead of the most related content. After further investigation, "Louder" outshines "Don't Wanna Go Home" with more credible sources such as BBC.com.