New texts reveal Cameron and Brooks’s close relationship

In a message obtained by the Mail on Sunday, the prime minister thanked Mrs Brooks for letting him ride one of her horses, joking it was “fast, unpredictable and hard to control but fun”.

In another the journalist, who faces trial in connection with the phone hacking scandal, praised Mr Cameron’s speech to Tory conference, saying: “I cried twice.”

The playful texts are apparently part of a cache of texts and emails handed to Lord Justice Leveson’s media standards inquiry.

Few have been made public so far – sparking accusations from Labour that they are being covered up.

Labour MP Chris Bryant has challenged Mr Cameron to publish all the material himself, suggesting he was delaying because it was “too salacious and embarrassing”.

This leak sheds further light on the close relationship between Mr Cameron and Mrs Brooks, who live near each other in Oxfordshire.

Mrs Brooks told the Leveson Inquiry earlier this year that Mr Cameron signed some of his missives to her “LOL” – mistakenly thinking it meant “Lots of Love” rather than “Laugh Out Loud”.

Brilliant speech. I cried twice. Will love ‘working together’ Rebekah Brooks

Both of the messages disclosed by the MoS were sent in October 2009, shortly after Mrs Brooks left her job as editor of The Sun and became chief executive of News International, which owns the paper.

After his conference speech, Mrs Brooks texted: “Brilliant speech. I cried twice. Will love ‘working together’.”

Questions about Mr Cameron’s close links with Rupert Murdoch’s media empire, and Mrs Brooks in particular, came to the fore after the phone hacking row erupted.

In her Leveson evidence, Mrs Brooks said that at the height of the scandal in 2010 he sent a message through an intermediary urging her to “keep your head up” and expressed his regret he could not be more loyal in public.

Lord Justice Leveson is believed to have received a large amount of correspondence from the Prime Minister, Mrs Brooks, and former Downing Street communications chief Andy Coulson.

The horse CB (Charlie Brooks) put me on. Fast, unpredictable and hard to control but fun David Cameron

However, the inquiry’s lead counsel Robert Jay QC has indicated that only “relevant” documents will be released.

Mrs Brooks and Mr Coulson, an ex-editor of the News of the World, are among those facing trial for conspiracy to access voicemails.

In a separate case, Mrs Brooks and her husband are among a group charged with conspiracy to pervert the course of justice.

A Downing Street spokesman said: “The prime minister has always been happy to comply with whatever Lord Justice Leveson has asked of him.”