Police said the thieves targeted cars parked in London and Essex parking garages by using remote-controlled technology to block locking systems, then got into the cars to get information needed to make keys and placed global-positioning systems in the cars, The London Evening Standard reported.
The thieves, police say, then tracked the vehicles and stole them.
The Standard said the thieves were to be sentenced in court Friday.
"This was the most extensive and complex case we have dealt with in recent years," said Inspector Paul Fuller of Scotland Yard's stolen vehicle unit.
The ringleader of the thieves, Alan Watkins, 42, was linked to the sale of at least 170 stolen cars worth more than $4.2 million, authorities said.
The thieves searched the Internet for cars exported to Cyprus then found similar vehicles in London and Essex, police said.
The stolen cars were then given new identities of vehicles in Cyprus and sold in Britain, the Star said.
Watkins of Witham, Essex, admitted to conspiring to steal and conspiring to handle stolen goods and possession of a stun gun and pepper spray.
Lee Fullick, 51, of Ingatestone, Essex, who police said helped clone the stolen cars, pleaded guilty to two counts of conspiring to handle stolen goods. Sukvinder Matto, 35, of East Ham admitted conspiring to steal.