Prime minister Tony Blair is among 136 people to have been questioned as part of the investigation following an official complaint by the Scottish National party, which claimed that a 1925 law prohibiting the sale of honours had been breached.
There is no suggestion of Mr Blair having committed any offence and he was not questioned under caution.
But the prime minister's close ally Labour fundraiser Lord Levy has been arrested on two occasions, along with parliamentary aide Ruth Turner and city academies advisor Des Smith.
All three deny any wrongdoing.
On today's developments, a Metropolitan spokesperson said: "It is now a matter for the CPS to consider the evidence, advise us on whether any further enquiries are necessary and whether any charges should be brought."
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