Electoral watchdogs are meeting with police and prosecutors in a bid to ensure they do not run out of time to launch possible criminal investigations into Conservative campaign spending on the 2015 general election.
Tories face claims that accommodation costs of activists bussed into key constituencies around the country should have been recorded under individual candidates' limits, rather than as part of the national campaign.
The Electoral Commission believes its ongoing probe into alleged breaches of reporting obligations will take at least another month - taking it past the one-year time limit for launching criminal proceedings.
It is meeting with police forces covering the constituencies involved and the Crown Prosecution Service to ask them to seek an extension to ensure the door is not closed.
Claims about the Conservatives' general election spending - as well as that at three parliamentary by-elections - were first raised by Channel 4 News.
The party blames an "administrative error" for failing to register some accommodation costs.
But David Cameron insists it was right to include such expenditure as part of the national campaign rather than against the limits imposed on individual candidates.
Bob Posner, director of party and election finance and legal counsel at the Electoral Commission said: "The police and the CPS both have the power to apply to the courts to extend the time limit on bringing criminal prosecutions for electoral offences to allow for full investigations to take place. We have requested that they consider doing this."
The commission said it did not take any view as to whether the party should be pursued under the Representation of the People Act (RPA) 1983, which regulates candidate spending.
But if no extension is sought, the ability to do so will expire a year after the submission of returns - which had to be with the Electoral Commission within 35 days of the election on May 7 2015.
An extension can be sought by the Director of Public Prosecutions.
Making a false declaration in relation to candidate spending carries a punishment of up to a year in jail and/or an unlimited fine - and anyone found guilty is barred from standing for election as an MP or holding elected office for three years.
No police investigation has yet been launched but the commission said it seemed "sensible for the criminal justice agencies to retain the ability to take action should appropriate evidence come to light as part of the commission's own investigation".