We have reached endgame. Over the next two days the Leveson Inquiry hears evidence from Andy Coulson and Rebekah Brooks, testimony that – if you believe an increasing number of commentators – could be hugely damaging to David Cameron.

Over the weekend the former editor of The Sun, Kelvin MacKenzie, revealed that he had placed a £1,000 bet on the prime minister to be gone by the end of the year. This seemingly outlandish wager has been the cause of much consternation around Westminster over the last few days, and with good reason. MacKenzie retains a close personal relationship with Rupert Murdoch - indeed he is believed to be Uncle Rupert’s favourite editor. Just this March the man who worked under Murdoch for several decades insisted, “I know Rupert, I really do”.

And it’s not just the man at the top who MacKenzie counts among his friends. While the Fleet Street veteran may not be on the best of terms with his former colleague Rebekah Brooks, MacKenzie is one of the most well-connected men in the business. He will have had the ear of those privy to News International’s deepest and darkest secrets, and he may well know what else there is to come out about the company’s relationship with Cameron & Co over the next two days. For Kelvin MacKenzie to bet £1,000 on Cameron’s demise, he must know something. And that is very worrying news for the prime minster.

James Murdoch’s evidence to Lord Justice Leveson showed us how, with the touch of a button within News International, a cabinet minister was apparently brought to heel. How Jeremy Hunt survived is beyond most pundits, indeed, he is not out of the woods yet. The release of thousands of text messages between Cameron and Brooks – unredacted – has the potential to be a devastating blow. We know that that the pair were riding partners and enjoyed Christmas dinner together, but insiders believe it went far further than that. Prospect magazine’s James Macintyre hints that the texts will reveal a ‘big bombshell’. That is hardly a surprise. The Labour leader Ed Miliband is well aware of what is coming; his attempt yesterday to widen anger at Cameron’s involvement with the Murdochs beyond the Westminster village is no coincidence.

The next two days could be Cameron’s most challenging since he took office. Either Coulson and Brooks will protect their old friend, or the Prime Minister will end up fighting for his political life. Kelvin MacKenzie thinks he worked out which way it’s going to go. And say what you like about Kelvin, but he would know.

Alexander Wickham is a freelance journalist and blogger who writes for The Independent, amongst others. He tweets at @Wickham_A

Tags: Andy Coulson, David Cameron, Kelvin MacKenzie, Leveson inquiry, Rebekah Brooks