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Historic Royal Palaces, the charity which maintains a number of royal palaces including Kensington Palace and Hampton Court, has apologised after its Twitter account sent out a message in support of the Conservative manifesto.

The tweet, which appeared briefly this morning before being deleted, read:

"This #ConservativeManifesto focuses on the people's priorities. #VoteConservative to get Brexit done, invest in our NHS, put more police on our streets, and properly fund schools. Share now: vote.conservatives.com/our-plan."

The charity says the tweet was posted accidentally.

It explained that Twitter's algorithm sometimes serves up content from accounts your followers have engaged with.

"In this instance," a spokesman said, "a tweet appeared on Historic Royal Palaces feed with a button that, if pressed, pastes that content into a new tweet. This button was pressed entirely accidentally, creating a tweet which was shared with followers of @HRP_Palaces."

The charity says it is an independent, politically neutral organisation and deleted the tweet as soon as the mistake was spotted.

The ³ÉÈË¿ìÊÖ learned about the tweet from a reader who sent it to our project tracking the way election adverts are targeted.

A ban on paid political ads on Twitter came in last Friday but campaigners are working hard to spread messages via their followers.

Facebook remains the focus for paid political advertising, with all of the main parties and a number of non-party organisations buying ads.

Sir Tim Berners-Lee has called on Mark Zuckerberg to stop selling targeted political adverts. He told the ³ÉÈË¿ìÊÖ it was not fair "to risk democracy by allowing all these very, very subtle manipulations with targeted ads which promote completely false ideas".

Please get involved - if you get an election ad on Facebook or any social media platform, send a screenshot of it and the Why Am I Seeing This Ad message to election.ads@bbc.co.uk, external.