A day after Amarinder Singh gave him top billing in his bitter resignation letter to Sonia Gandhi, Navjot Singh Sidhu railed at the former Chief Minister, calling him a "fraud, coward and spent cartridge".

Sidhu, the Punjab Congress chief, accused Amarinder Singh of raising allegations of corruption that he himself did not act on, out of cowardice.

"The Captain is a spent cartridge. He is a fraud. Now he claims ministers were involved in illegal mining - then why didn't he act? He is a coward," Sidhu told reporters today.

"Now he is saying that these guys robbed the treasury. Was he sleeping? He could see that loot was going on and he didn't do anything? This is a sign of cowardice," he said.

He also remarked that "not even a councillor had left" the Congress, not even his wife Preneet Kaur. "Ask him if Preneet Kaur will quit the Congress," he said, referring to the former Chief Minister's wife, who is a Congress Lok Sabha MP and a former Union Minister.

Amarinder Singh was forced to quit as Chief Minister in September after months of acrimony and sparring with Sidhu.

In July, Sidhu had been appointed Punjab Congress chief as part of the party's attempts to broker peace between the feuding leaders. But any truce reached at the time was short-lived.

Amarinder Singh made his split with the Congress, his party of five decades, official yesterday and announced a new party, the Punjab Lok Congress.

In his seven-page exit letter, Amarinder Singh called the cricketer-turned-politician "an acolyte of the Pakistani deep state" and "a person of unstable mind".

The Captain accused Sidhu of "using the filthiest and most vile language" against him and wrote: "Sidhu's only claim to fame was that he would abuse me and my government on a regular basis. I am old enough to be his father but that did not stop him from using the filthiest and most vile language against me, both publicly and privately."

The Captain also expressed his dismay with Rahul Gandhi and Priyanka Gandhi Vadra for backing Sidhu. "I told you at the time that Sidhu is a person of unstable mind, and you will one day regret this decision... I am sure you must be regretting it now..." he wrote.