Cardiff's lawyers allege in a five-page letter that Palace's sporting director Iain Moody tried to obtain information about the Welsh club's starting line-up before the game this month, the BBC said.

Moody joined Palace after being sacked as Cardiff's head of recruitment in October.

According to the BBC, Cardiff allege that Moody succeeded in discovering their line-up for the April 5 game, thereby breaching league rules.

"Cardiff states that clubs should act in good faith to one another and calls into serious question the integrity of the match," said a report on the BBC website.

"The club says Crystal Palace cheated and wants the Premier League to take serious action."

The Premier League confirmed earlier this week that it is investigating Cardiff's complaint.

British media reports last week claimed that Cardiff had sacked one staff member and were preparing to discipline another over the matter.

However, Moody denied the allegation that he had tried to find out about Cardiff's team, telling The Sun newspaper: "That is incredibly, extraordinarily untrue. That is untrue, completely untrue."

The BBC said Palace manager Tony Pulis had declined to comment on the reports.

Palace look set to avoid relegation after a 3-2 win at Everton on Wednesday took them to 40 points. Cardiff are three points from safety with only four games of the season remaining.