Tory election expenses row: How bad could it get?

How many MPs are under the spotlight?

Two dozen are believed to be under investigation by their local police forces, who have until later this year to decide whether charges should be brought.

They include Craig Mackinlay, who beat Nigel Farage in South Thanet after a big operation by Tory campaigners. He was understood to have been interviewed by police last weekend for six hours.

Previous investigations by Channel 4 News and the Daily Mirror have highlighted others.

Sky News has seen a list of more than 30 Tory MPs who are implicated, although at least two are believed to have been cleared by local police forces.

Some of the MPs are much more concerned than others. Some had a visit by the campaign "battle bus" for just one morning and say they had enough money in local spending that they could have covered it - if they had known it should be registered locally. Others are said to be "scared" about the investigation.

What has Sky News found out?

That recriminations are flying within the party about who is to blame, as an official investigation looms.

A leaked email from Tory MP Karl McCartney, who narrowly beat Labour in Lincoln, refers to the situation as a "mess" which he predicts will result in a "media s***storm".

He blames "clever dicks" at Conservative central office for the spending row, and says MPs are being hung out to dry while Tory officials who masterminded the campaign are "covering their backsides".

Party chairman Patrick McLoughlin has been in touch with Tories affected, and held his first showdown meeting with them on Tuesday. The party has also paid for a lawyer for them.

Mr McCartney claims central office has seen a draft report from the Electoral Commission into the affair ahead of publication and refused to reveal its contents but Conservative sources deny this.

What happens next?

The Electoral Commission is investigating the Conservative party's national spending, and spending on three by-elections in 2014, and is due to report in the coming weeks.

It emerged last year that some £38,000 of spending had not been declared to the watchdog, which the Conservatives put down to an "administrative error". A £20,000 fine could be imposed.

There are also more than 20 separate police investigations into MPs and their election agents and whether they knowingly made a false declaration.

Election agents who filed the campaign return - how much was spent in their local area - face jail. Some MPs have told Sky they expect to be cleared because they closely followed guidance from headquarters which they believed was correct.

How bad could this get for the Conservatives?

The one the Tories are particularly worried about is South Thanet, where Mr Mackinlay beat Mr Farage by 2,000 votes in a contest the Tories were desperate to win.

The campaign return came in at under the £15,000 local limit, imposed to ensure a level playing field. But it has been claimed another £18,000 was spent at nearby hotels.

If any police forces decide there is a case to answer, they will pass a file to the Crown Prosecution Service and the case will go to court.

This could result, eventually, in contests being rerun and the prospect of a raft of by-elections for a Prime Minister with a 12-seat majority and tricky Brexit negotiations to navigate.

Other Tory MPs are simply worried it has dragged on for so long, and hope they will be able to clear their names well ahead of the next general election. Whenever it comes.