Andy Burnham should publish all details of his meetings with Manchester City ’s owners, the Abu Dhabi United Group (ADUG), and declare all hospitality he has accepted at the Etihad Stadium, the Liberal Democrats have said.

The prime minister was roundly criticised this week for saying he would be “really concerned” if City’s Abu Dhabi owners sold the club after the club was found to have breached the Premier League ’s financial rules by an independent commission, crediting them with being “a huge partner in the building of modern Manchester”.

Downing Street was forced to issue two clarifications of his position on Thursday, with a spokesperson for the PM insisting the guilty verdict against Manchester City is “serious”.

Mr Burnham’s comments drew criticism on social media and shadow sports minister Louie French called for the government to “keep politics out of football”, with the case set to proceed to an appeal board and a sanctions hearing.

Now, the Liberal Democrats have drafted a strongly-worded letter to the prime minister, criticising his defence of City as “extraordinary”.

In the letter, seen by the Guardian , the party’s spokesperson for culture, media and sport, Anna Sabine, wrote: “As you will know, an independent commission has found Manchester City guilty of 114 charges of breaching financial rules over a timeframe of nearly a decade, including the use of ‘sham contracts’ and schemes to disguise more than £830m of funding.

“Despite this, your response was to thank the club’s owners for their work and describe the findings as ‘contested’ and that it was ‘wrong to jump to a conclusion’. It is extraordinary that a prime minister would use his position to call into question the findings of the independent investigation, and risk undermining trust in the Premier League’s processes.

“This has been a difficult year for football’s reputation. Fifa’s conduct around the World Cup has already raised serious questions about integrity in the game we love. At a moment like this, fans expect their prime minister to stand up for the rules in place, not to appear to side with a club found guilty of breaking them.”