Investigations have been launched into the spending returns of both the lead campaigns in last year’s EU referendum, Stronger In and Vote Leave, the Electoral Commission has announced.
Precise details of what is to be investigated have yet to emerge.
Details of spending by the main campaign groups in last year’s EU referendum are being published by the official elections watchdog.
The Electoral Commission will set out details of organisations and individuals who spent over £250,000 during the campaign period.
Under election law, anyone who intended to spend more than £10,000 during the course of the campaign period from April 15 to June 23 was required to register with the commission.
The commission has already released details of £4.5 million of spending by 46 registered campaigners who spent up to £250,000, as well as two others who spent over £250,000 but submitted their returns early.
A further 47 registered campaigners have declared that they did not spend over £10,000 and were therefore not required to submit a return.
Under the referendum rules, the two official campaigns were each permitted to spend up to £7 million during the campaign period.
Most other registered campaigners were restricted to £700,000 - although there were larger allowances for political parties which gained over 5% of the vote in the 2015 general election, depending on their vote share.