Most people dressed as Smurfs

According to Official Guinness Records,

The most people dressed as Smurfs was 2,510 and was achieved by Jokers' Masquerade with the help of Swansea University at Swansea Oceana in Swansea, UK, on 8th June 2009.
Faces, arms and legs must be painted blue to be counted towards the total.

For a complete list of 2009 records, please visit 2009 Guinness Records in United Kingdom.

Other United Kingdom records that might interest you:

• Fastest time to carve a turkey
• Most push ups (finger tips) in one minute
• Longest dog tunnel
• Largest trousers
• Thickest book published
• Most completed journeys from Land's End to John-O'-Groats
• Largest parade of Mini cars