Can I extend my 60-day visa exemption for an additional 20 days in Thailand?

A British national in Thailand with a 60-day visa exemption can apply for a 30-day extension at their local immigration office. It is not possible to extend the visa online. The extension requires documentation including two photocopies of the passport, a TM30 form from the hotel, and a spare passport photo. The application should be made at least two weeks prior to the expiration of the current visa.