P Chidambaram is spending his 74th birthday in Tihar jail in Delhi. (File)

Highlights P Chidambaram is spending his 74th birthday today in Tihar jail

To mark the day, his son Karti has used an open letter to attack centre

He also takes aim at the government on the slowdown

Former Union Minister P Chidambaram is spending his 74th birthday today in Tihar jail, where he was sent on September 5 in a corruption investigation. To mark the day, Karti Chidambaram has used an open "letter" to his "Appa" to take several sharp digs at the government.

The letter gets down to business with its opening line referring to the "56-inch chest" comment by Prime Minister Narendra Modi during his campaign in 2014: "You are turning 74 today and no 56!!!" Karti Chidambaram then refers to a range of subjects from the Chandrayaan 2 launch to the growth slump and Jammu and Kashmir to bring his father up to speed, as he calls it.

"...we wish you were back home to cut a cake with all of us. But of course, in today's day and age, turning 74 is nothing compared to turning a 100 days old," writes Karti, a Congress MP, snarking about the blitz to mark 100 days of the Modi government.

He writes about the "drama" at the Chandrayaan 2 mission's attempt at a moon landing and the loss of contact. "No, not the drama of the lander losing communication, but the big drama a little after that. ISRo chief Dr (K) Sivan, our fellow Tamilian from Kanyakumari, was visibly upset and the Prime Minister was at hand to offer his arms and comfort him with his iconic head grab. I sincerely hope our Prime Minister pegs the achievements of our ISRO scientists a little above what his bhakts believe - that India's Space Programme, along with plastic surgery and aviation, was created thousands of years ago...and not by ISRO. In fact, last week Piyush Goyal even snatched the theory of gravity away from Newton and pooh-poohed Einstein," he says in the two-page letter.

My letter to my father @PChidambaram_IN on his birthday #HBDPChidambarampic.twitter.com/LCTV2Br4Ha — Karti P Chidambaram (@KartiPC) September 16, 2019

Taking aim at the government on the slowdown, Karti refers to the six-year low in GDP growth, the auto sector crisis and the "astute insight" of "your successor twice removed Ms Nirmala Sitharaman" on millennials preferring ride-sharing apps.

On the security restrictions in Jammu and Kashmir since August 4 to prevent a backlash over the centre ending special status to the state, he writes: "Only you will understand the true plight of the Kashmiris. Because both of you have been locked down unfairly. Though you are better off than the people of Kashmir who are still under a government-imposed communication blackout."

The letter goes on to recount international developments, each appended with a jibe at the government. Even Rafael Nadal's US Open win inspires one.

"...It was something else to see him triumph on a surface that has repeatedly been unforgiving and cruel to him. Had you been at home, we would have definitely watched the match together. Rafael Nadal then shook hands with Medvedev, the way civilized opponents should. Not get vindictive and punish them for no cause," says Karti's letter.