Jeremy Corbyn’s three sons have paid tribute to their father following Labour’s worst defeat in more than 80 years, while condemning the “despicable attacks” he has faced throughout his leadership.

The Labour leader’s youngest son, Tommy, 25, with his brothers Seb, 27, and Benjamin, 32, posted a statement on Twitter expressing pride in their father, who they said had produced the “most wonderful manifesto this country has ever seen”.

They described him as “honest, humble and good-natured” within a “poisonous world” of politics, and pointed towards “despicable attacks filled with hatred” as the reason for his undoing.

“He took on an entire establishment. This meant the attacks from all sides intensified and became even more poisonous while he was leader. We’ve never known a politician to be smeared and vilified so much,” they said.

Jeremy Corbyn says he will stay as Labour leader after election pounding Read more

“Jeremy has dedicated each day of his political life for the less fortunate amongst us. Unwaveringly, he has fought and campaigned for people who suffer and people in hardship.”

The Conservative party secured its biggest majority since 1987 in the general election. Many seats in Labour’s historic heartlands – constituencies such as Bishop Auckland, Redcar and Great Grimsby – turned blue, rejecting Corbyn’s vision.

The brothers said that the defeat “hurt” but – despite the crumbling of Labour’s “red walls” – they believe the time is still to come for their father’s policies.

“To assume that the ideologies he stands for are now outdated is so wrong. In the coming years we will see that they are more important than ever,” they said. “Thank you to every person who saw his vision and supported it and supported him. From the three proudest sons on the planet, please continue the fight.”

Play Video 2:19 Jeremy Corbyn says he will stay as Labour leader until next year – video

As the results emerged, Corbyn gave a speech at his count, in Islington North, saying he would not lead the party into the next election. He later said he would step down as leader in the “early part of next year,” following a meeting of Labour’s national executive committee.

He said he was “obviously very sad at the result we’ve achieved and very sad for colleagues who have lost their seats in the election and very sad for many people in this country who will now have a government that is continuing policies of austerity, and many of the poorest communities will suffer very badly from the economic strategy that I suspect the prime minister will take forward”.