Pakistan's former high commissioner to the United Kingdom and PPP loyalist Wajid Shamsul Hasan passed away in London on Tuesday, party leaders said.

In a tweet, PPP chairperson Bilawal Bhutto-Zardari condoled Hasan's demise, saying an "immense source of strength and guidance for me left us today".

"Journalist, diplomat, democrat, family friend, good bye uncle Wajid," Bilawal wrote. "Nothing will be the same without you."

State-run APP news agency reported that Hasan passed away in London after a prolonged illness.

Bilawal also shared his text conversation with Hasan last year, in which the former diplomat had reported being unwell.

Senior PPP leader and Senator Sherry Rehman said she was "shocked, saddened" to hear of Hasan's passing.

"He spent a lifetime of devotion to democracy, human rights, free press and the PPP. What a loss!" she tweeted, extending condolences to his family and the broader civil society community that she said he had been deeply involved with.

PPP Central Information Secretary Shazia Atta Marri also expressed grief and sorrow over Hassan's death, saying his journalistic, diplomatic and national services would always be remembered.

Hasan had stepped down as Pakistan's high commissioner to the UK in April 2014 after serving in the office for six years.

He was at the time the longest-serving Pakistani envoy to the UK. This was his second stint there, having worked as the high commissioner from 1994 to 1996.

Hasan was the author of 'Bhutto Khandaan Meri Yaadon Mein: Wajid Shamsul Hasan Ki Nisf Sadi Par Muheet Yaadein'.

Translating to 'The Bhutto Family in My Memories: Wajid Shamsul Hasan’s Memoirs of Half a Century', this is an insider account of events centred on the Bhutto family, as narrated by someone who spent a lifetime associated with them. Additionally, the former diplomat in his book recounts memories of his own life and career trajectory, from starting out as a junior journalist to his appointment as the chairman of the National Press Trust.