A day of acrimonious industrial action at the BBC left the public broadcaster bracing for a wave of strikes by its journalists that could run on until Christmas.

A walkout by news journalists, including high-profile presenters Martha Kearney, Nicky Campbell and Fiona Bruce, took a string of programmes off air today – including Radio 4's Today, the BBC1 Breakfast programme and BBC2's Newsnight.

BBC executives battled to keep programmes on air during the first half of the 48-hour strike by the National Union of Journalists over pension cuts. Helen Boaden, the director of BBC News who is tipped as a future director-general, read out an item about the Phil Woolas election court verdict on Radio 4 in the lunchtime and six o'clock news.

Behind the scenes there was little sign of detente, with BBC insiders saying that the NUJ had fallen prey to "leftist influences" and that the broadcaster had no intention of sweetening a pension deal that has already been accepted by the broadcaster's other major union, BECTU, which represents camera crew and technicans.

Meanwhile, the NUJ is planning another 48-hour strike beginning on 15 November. Union leaders are also threatening further disrupution over Christmas, although no dates for future action have been set.

The BBC said its news output had been significantly less affected than it had expected – it was hoping to broadcast a full-length 10pm news bulletin tonight – despite around one in six staff choosing not to cross picket lines.

"No BBC services have been blacked out or gone off air," said BBC director general Mark Thompson in an email to staff. "However, a few programmes have been lost and our ability to deliver the normal scale and quality of news and journalism to our audiences here and around the world has been impaired."

However, the NUJ described the BBC's news coverage as "paper thin" and the strike as "completely solid".

NUJ general secretary Jeremy Dear compared Thompson's comments to Muhammed Saeed al-Sahaf, the Iraqi information minister at the time of the 2003 invasion. "When Mark Thompson says that this strike is having no effect on the BBC's service, it's a bit like Comical Ali standing outside Baghdad Airport saying there are no Americans in Baghdad as the troops swarm in."

At issue are planned changes to the BBC's final salary pension scheme. BBC executives say that the overhaul was necessary to cut a pension deficit estimated at between £1.5bn and £2bn, although the actual figure will not be known until next year.

Newsnight economics editor Paul Mason accused corporation bosses of "trying to steal our accrued pension benefits".

"We want a full objective valuation of the pension scheme and we want our managers to talk to us rather than engaging in a game of long-range insults," said Mason, who later confronted outgoing deputy director Mark Byford as he crossed the picket line outside the BBC's Television Centre in west London.

But the BBC has said its most recent pension offer, which has been accepted by three other unions at the BBC as well as Bectu, would be its final one.

The BBC People director Lucy Adams said: "It's quite difficult to see at the moment quite how we're going to resolve this. The deficit is at least £1.5bn, possibly higher. It would be negligent not to act now. We believe by not acting it would be negligent for staff and audiences."