Three other people were arrested in Tottenham, north London, at the same time as McLoughlin, police said.
The 54-year-old man from Tottenham, 45-year-old woman from Edmonton, north London, and 50-year-old man from Hackney were arrested on suspicion of assisting an offender.
All four are being questioned at Hatfield police station, Hertfordshire Police said.
More top news
Simon Lucy, 61, filmed hundreds of hours worth of footage on the London Underground network.
He delighted fans as he started off his performance playing his song 'Ordinary People'
Craig Mackey delivered a message to tech giants which have come under fire for hosting extremist material.