Christopher Steele, 52, who runs London-based Orbis Business Intelligence, was named in reports as having compiled the file on Mr Trump.
According to the Daily Telegraph UK, Steele fled his home in Surrey yesterday fearing a backlash from Moscow after his identity was revealed online.
A neighbour told The Telegraph he'd asked for his cat to be looked after while he laid low.
"He asked me to look after his cat as he would be gone for a few days," said the neighbour. "I'm not sure where he's gone or how to contact him. I don't really know much about him except to say hello.We're all pretty secretive round here to be honest. All I know is he runs some sort of consultancy business."Steele is said to be a highly-respected Russian expert who spent many years in the British intelligence service before setting up his own private business.
Last night, senior British security sources revealed emergency measures were being taken to make Steele safe.
British newspapers and media outlets were being asked not to name him until after 10pm on Wednesday to give him some leeway so he could be made safe.
That means it is possible he was being transported to an emergency safe house - which may be in a different country