The revelation is likely to increase concern in Downing Street and the Conservative party about the seriousness of the investigations, which could affect several sitting MPs and even lead to election results being declared void if there are prosecutions.

Two dozen Tories are understood to be under police investigation over claims they overspent on their local campaigns during the 2015 general election in which spending limits are tight.

Karl McCartney, MP for Lincoln and one of those under investigation, wrote a bombshell email to the party chairman attacking the party’s handling of the controversy linked to its election “battle bus”.

In it, he wrote: “We didn’t create this mess, the clever dicks at CCHQ (Conservative Campaign Headquarters) did, and I don’t see their professional reputations being trashed in the media.”

Sky News can reveal:

:: An email sent to 30 Tory MPs claims the party has withheld a draft report it has already received from the Electoral Commission into the issue.

:: A second email to the party chairman claims Conservative Central Office was to blame for the expenses “mess”.

:: The MPs held a showdown meeting with party chairman Patrick McLoughlin on Tuesday afternoon to air their concerns.

:: MPs implicated in the row said they felt “scared” about the outcome of the investigations and believe Downing St is worried.

The spending row centres on the Tories’ use of an election battle bus to campaign in key seats, and whether spending on hotels and campaign material were incorrectly registered as national spending, which has much higher limits than local spending.

Meanwhile, Kent Police refused to confirm reports Tory MP Craig Mackinlay, who defeated ex-UKIP leader Nigel Farage in Thanet South, was questioned under caution last Friday over his expenses.

If Conservatives are found to have committed any offence, their political opponents could ask for the contests to be rerun.

Mr McCartney, a justice of the peace who was elected in 2010 and fought off a challenge from Labour in 2015, is said to be acting as an informal “shop steward” to the group of mainly newly-elected MPs implicated.

He wrote to colleagues last week saying Conservative Central Office (CCHQ) had received a draft report from the Electoral Commission, which has been investigating party spending for a year.

Mr McCartney said this information came from a Conservative-party appointed solicitor who is acting for the group, but claimed the contents of the report had not been shared with MPs.

However, a Conservative source denied officials had received the report.

Mr McCartney wrote: “I have made my disquiet and disbelief at this course of action pretty clear in a blunt email to the party chairman and the whips office overnight.”

In that email, also seen by Sky News, and addressed to Mr McLoughlin who is in the cabinet, he wrote that his colleagues “feel completely cast adrift by CCHQ/whips/the parliamentary party and left to fend for themselves”.

He added: “At what stage do you think you (the Party) might inform us that another media s***storm is coming? We didn’t create this mess, the clever dicks at CCHQ did, and I don’t see their professional reputations being trashed in the media much.

“The initial cock-ups, ‘strategy’ and ineptitude with regard to this issue that has so negatively impacted our: lives, standing in our communities, standing amongst colleagues, families and our regard for particular parts of the Party centrally, and were all of CCHQ’s making…need to stop.

“We are the ones who are now (and since the beginning as individuals have been) in the media spotlight and it might have been a little more reassuring and collegiate if the powers that be in our party perhaps tried to be a little bit more supportive and less interested in covering their own backsides.”

Mr McCartney asks why MPs were not warned about the Electoral Commission report, expected to be made public in the coming weeks.

He said none of the MPs have been questioned by the Commission and asked: “Who else has had a copy? And what are the ramifications of its current version and what if it accepts your feedback and rewrites whole swathes of their draft?”

He asked the party chairman for guidance on dealing with media inquiries, saying: “We do need a press release for national and local media interest. I would rather sing from the same hymn sheet.”

On his website, he wrote: “The Conservative Party advised us that the so-called campaign ‘battle buses’ were, as at previous general elections and in keeping with the practice of both the Labour Party and Liberal Democrats, a national campaign expense.

“This meant that they were not to be declared in our own election expenses.”

Another of the MPs in the group, elected in 2015, and under police investigation said they firmly believed the spending was correctly registered.

The MP said: “People are scared, this has been hanging over us for more than a year. I absolutely believe it was legitimately national spending in my case.

“Our solicitor which they have paid for agrees that the law is what it is and we haven’t broken it. But I think CCHQ have been quite complacent about how far it would go. No 10 is now very concerned about it.”