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
A round the world yacht race set off from London today on a year long journey which will see them circumnavigation the globe.
The shortlist for the ugliest buildings in the country has been finalised with four of them coming from London.
Hundreds of thousands of people turned out for the Notting Hill Carnival today with the weather just managing to hold off.