The episode in question, episode 7 of series 3, was aired on Monday 8th December 1980 (IMDB). The sketch linked by the OP was at the beginning of the show (see YouTube video and full episode guide from comedy website Some of the Corpses Are Amusing).

The question might prompt a double-take. Not the Nine O’Clock News was a satirical comedy show, and the sketch suggested The Guardian, a centre-left or left-wing mainstream newspaper, had praised former British Union of Fascists leader Oswald Mosley. It’s simply absurd comedy, isn’t it? Or is it?

Oswald Mosley died on 3 December 1980. The Guardian ran a short obituary on the front page the next day, 4 December. It was written by Martin Walker, who also wrote a longer article about Mosley inside the paper.

Obituary: aside from purely factual details, he is described as having been

the dominant young man of his political generation. His frustration at Labour’s unwillingness to accept radical Keynesian solutions to economic problems to reduce unemployment in 1930 led him to found his own party.

[A factoid which may surprise those who categorised Mosley as having only ever been involved with Fascism. The Not the Nine O’Clock News team were mostly born in the 1950s. As educated people may well have been aware of this info about politics a couple of decades before they were born, though it may have felt somewhat incongruous, having only ever been contemporaneously aware of Mosley as an old Fascist.]

riotous public meetings and street battles as his Blackshirts tried to march through London discredited a party which never achieved electoral success...
His opposition to the war against Hitler in 1940 led to his imprisonment in 1940 with his wife and other Fascist leaders. He was released in 1943 on medical grounds, having been detained in a comfortable flat at Holloway prison with his wife, Diana Mitford.

At time of death, he was preparing to take part in a TV programme, in which he planned to say

that Britain needed a national government during the present crisis, and that above all, Britain must never leave the EEC.

It concludes:

He had always claimed that his ideas were right, but that they were expressed at the wrong times.

[A few bits WRT idea of “present crisis”, British unemployment was at its highest since 1935, the economy was in recession, the government low in the polls, and the strikes which had become frequent under the Labour Callagham govt had been ongoing, with a major strike by steelworkers earlier that year. Other headlines on the front page that day refer to the US monitoring Soviet plans to invade Poland, where the Solidarity protests were beginning, and to a probable IRA attack on a diplomat.]

Some quotations from the longer feature article:

"He was always convinced that he was right, that he and he alone could save and lead the nation"

(the closest IMO to “dynamic”)

"It was the appalling brutality of his stewards at the Olympia meeting of 1934 that lost him the support of key sections of the Conservative Party"

Still referring to the 1930s:

“He tried a campaign to win over the slump-hit middle classes and workers in the northern cotton towns, and dropped it as it began to achieve some success.”

(the closest, IMO, to championing “the unemployed and other underdogs”)

“After the war there were increasingly pathetic attempted comebacks…”

On Saturday 6th December, The Guardian published a letter signed “Jeffrey Hamm (Secretary to the late Oswald Mosley)”. It begins:

"May I be permitted to comment on Martin Walker's extremely fair obituary of Sir Oswald Mosley?"

The remainder of the letter is about events of the Battle of Cable Street, taking issue with certain points of the coverage of that.