David Davis, the Secretary of State for Exiting the European Union, has called for UK NGOs to campaign against EU preparations for a "no-deal" Brexit.

Davis made the call in a letter last month to Theresa May, the Prime Minister, warning that EU measures to prepare for a scenario in which the UK left the EU without a securing a trade deal could already be damaging British businesses.

Sue Tibballs, chief executive of the Sheila McKechnie Foundation, which supports campaigning by charities, said the government needed to give a clear view on whether it was comfortable with charity campaigning.

Davis’s letter, which was leaked to the Financial Times newspaper, said organisations should be encouraged to lobby the EU if they were likely to be affected by EU planning, and specifically mentioned NGOs.

Davis said he had instructed his officials to work more closely with UK business. "This should also include encouraging UK companies to lobby more actively, identifying non-UK businesses and NGOs or wider EU interests that might be adversely affected by such actions and encouraging them to lobby either independently or with UK partners."

In 2016, the government attempted to introduce a clause in all government grant agreements that would prevent charities from using the funds for lobbying.

The policy was subsequently put on hold before being significantly watered down after outcry from voluntary sector bodies.

Tibballs said Davis’s call for charities to lobby the EU was an example of the "mixed messages" charities received from government about campaigning.

"WWF was recently praised by Michael Gove [the environment secretary] for its campaigning work on the ivory trade, but then from other parts of government we get the message that they believe charities should not be campaigning," she said.

"There are mixed messages that create a profound level of confusion and anxiety. It would be incredibly helpful if they could give a clear view."

She said part of the problem was that advocacy work, raising public awareness and seeking to give policy input were often grouped together under the heading of campaigning.

"It is interesting that the letter even uses the term ‘lobby’," she said. "Does this call for NGO lobbying extend to those in receipt of public funds? According to nfpSynergy research, 50 per cent of Conservative MPs don’t think charities in receipt of public funds should lobby. Maybe they view it as a problem only when the lobbying is directed at them.

"You could get the impression that the government is comfortable with charity campaigning – including lobbying – when it suits it, and not when it doesn’t. It is on an issue-by-issue basis, you might say."