Detectives have been looking into expenses for several months
Police investigating alleged abuses of parliamentary expenses have referred four cases to prosecutors.
Detectives have been looking into several cases since the allowances scandal erupted over the summer.
The identities of the four parliamentarians, who come from both the House of Commons and the House of Lords, have not yet been revealed.
The Metropolitan Police said "a small number" of further cases were still being investigated.
There have been no arrests during the investigation, although some people have been interviewed under caution, the BBC understands.
Director of Public Prosecutions Keir Starmer must now decide whether there is a realistic chance of convicting the four and what charges, if any, to bring.
If any politicians are found guilty of fraud or false accounting, they could face maximum penalties of 10 or seven years in prison.
A Scotland Yard spokesman said: "The Metropolitan Police Service has today delivered four main files of evidence relating to parliamentary expenses to the Crown Prosecution Service."
He added that these would "now be subject to CPS consideration on whether there should be any charges".
The spokesman also said: "A small number of cases remain under investigation."
A Crown Prosecution Service spokesman said: "Any decisions on whether or not there should be any charges in relation to these files will be made as quickly as is reasonably practical.
"Since a number of other cases in relation to parliamentary expenses are still under investigation, it would be inappropriate to comment any further at this stage."