Taking NSAIDs (Nonsteroidal anti-inflammatory drug) in a month prior to chickenpox is associated with a five times higher risk of complications. Paracetamol is associated with a 50% increase in the risk of complications.
Other studies determined that:
1) Taking ibuprofen in a month prior to varicella is associated with a three times higher risk of skin superinfections.
2) Ibuprofen is associated with an 11.5 times increase in the risk of necrotizing fasciitis.
3) Ibuprofen is associated with a 3.9 times increase in the risk of group A streptococcal infections. 
I recently graduated from a medical school and in the 6 years of studying, despite repeated encounters with varicella, I have never heard that anti-inflammatory drugs complicate the course of chickenpox. So I did not take the Daily Mail article, warning against the use of ibuprofen during chickenpox, seriously.
However, I learned that the Ministry of Health and other medical associations really do recommend avoiding ibuprofen during varicella.
It is strange that no one warned me about it during the whole period of my studies. Of course, the information is available, if you go looking for it, but since ibuprofen is such a common medicine, it would be beneficial to have this information covered more widely.