The letters have prompted Labour councillors to start paying pounds 10 a week into a special legal fund to seek advice should the district auditor threaten them with surcharge or repayment of hospitality.
Most of the recipients of the letters are councillors and include virtually all the leading councillors on the Labour-dominated council purged from their committee positions after the allegations of unauthorised foreign trips and boozy lunches were first reported in The Independent earlier this year.
In addition, a few former councillors, including the ex-leader Gordon Gallimore, and senior officers, among them the former chief executive, Doug Hale, are known to have received letters relating to a trip to Germany.
Several councillors, including at least one Tory, have started repaying the cost of hospitality received in an effort to allay criticism, but police sources have indicated that this will not exempt them from prosecution should investigations reveal that a crime has been committed.
In February, the district auditor first revealed his concerns that trips to many parts of the world, including China, Poland, Germany and the United States may not have been properly sanctioned by the council.
There are two other inquiries into allegations of wrongdoing at the council. The police are focusing on allegations that some developers were given favourable treatment while the council itself is also looking at mismanagement.
While the letters suggest that the recipients will be criticised in the report, the aim is to give them one last chance to explain their conduct. A council source said: "Many of the councillors are appalled about what they have been sent and are hoping they can meet the district auditor to discuss the allegations."
The district auditor has given the recipients until the end of the month to respond but as it is the holiday period, they will probably have a couple of weeks' grace.
The Labour group on Doncaster council voted on Monday to request that its 58 members contribute pounds 10 per week out of their own pockets, up to a maximum of pounds 100, to enable the group to seek legal advice collectively.
While most have agreed to pay the amount, several have refused. One refusenik said: "I've done nought wrong, so I'm not paying. I don't see why they are getting joint legal advice, when each case is different depending on how many trips they went on."Reuse content