What is the nearest immigration office to Chalong, Phuket for a visa extension and what documents are required?

A UK passport holder planning to visit Chalong, Phuket for 75 days can apply for a visa extension. There are three immigration offices in Phuket: the main one in Phuket town, the one at Blue Tree water park, and the one in Patong. The main office in Phuket town is advised for easier access. When applying for the extension, one should prepare necessary documents, although specific document requirements were not detailed in the comments.