The search for a farmer who has been missing for more than a month could take "a number of weeks", according to the police.
70-year-old William Taylor was last seen at his home in Gosmore, North Hertfordshire, at around 9pm on Sunday June 3. It was his 70th birthday on June 11.
Over one hundred specialist volunteers are now searching the nearby farmland after police increased the operation area to a 1.7km (1.05 miles) radius from William's farm.
His son Richard Taylor has said the situation is "unbearable". “If anyone out there knows anything about my dad’s whereabouts please contact the police,” Mr Taylor said.
He was last seen just days after reporting that his Land Rover had been deliberately set on fire.
The conditions have been described as “difficult” by the police, with the ongoing heatwave and the height of crops, described as waist-high, proving barriers.
A police spokeswoman said: “Today we’re doing further searches, specialist trained officers are going through the middle of the fields, just to make sure we haven’t missed anything.
“This is so we can just make sure William isn’t one of the fields.
“It’s really difficult; it’s very hot, and the oat crops are fairly mature, so they are waist high.
“There are a lot of fields so it is going to take a fair amount of time.”
Officers are searching farmland as part of the investigation into the whereabouts of #missing William Taylor. He was last seen on Sunday, June 3rd in #Gosmore. We have issued this public appeal. Please RT and call 101 with info. If you see William call 999 https://t.co/QaFsKGFECE pic.twitter.com/B3FR1NWlY1
— Herts Police (@HertsPolice) July 9, 2018
William is described as white and around 5ft 11in tall, and is of a medium build with short grey hair.
He was last seen wearing a baby blue-coloured shirt, jeans and black wellies. It is believed that William may be wearing a navy blue boiler suit.