Police have arrested 30 climate activists after a major bridge in central London was blocked by a sit-down protest.

The arrests on Lambeth Bridge came after Public Order Act conditions were imposed on the protest, which had been held in support of nine Insulate Britain campaigners who were jailed this week.

The bridge had been shut to traffic for a number of hours on Saturday by the sit-in, which initially involved up to 250 people who had marched from the Royal Courts of Justice.

Referring to Public Order Act conditions imposed on the protest, the Metropolitan police said: “Lambeth Bridge has now been reopened, 30 arrests were made for breach of S14 conditions.”

The force also said that Vauxhall Cross, where some of the demonstrators had moved, had reopened.

Earlier, climate protesters blocked the two London bridges as part of a demonstration against the jailing of nine Insulate Britain activists.

Members of the group were sentenced this week after breaching a court injunction in place to stop further road blockades that have caused serious disruption for motorists since September.

Campaigners stopped traffic on Lambeth Bridge, which crosses the Thames between Westminster and Lambeth, just after 2.10pm on Saturday. A sit-down protest forced police to divert traffic to other routes.

Earlier on Saturday evening, the Met imposed public order conditions on the protest and urged the remaining protesters to leave. Four of the protesters had glued themselves together.

The public order notice said the group have “no identified organiser” and “warm clothing, food, seats” and if they fail to leave, could face arrest.

An offshoot protest also blocked Vauxhall Bridge, the next bridge upriver.

Gabriella Ditton, 27, who was taking part in the demonstration at Lambeth Bridge said she believed she would end up in jail for taking part in the protests. She has been arrested six times with the campaign group, once for breaking the injunction.

“I have known for a couple of years that the only thing that is going to serve us is civil resistance. I have faith in people coming together.

“Solutions to this crisis exist, we just need the political will to do it.”

Zoe Cohen, 51, who had travelled from Warrington in north-west England to take part, said: “I am angry, distraught and grieving for the huge amount of nature that we have already lost.”

She added that “ordinary people should not have to do this and risk prison”.

“Any disruption is microscopic to the suffering of millions of people who are dying now across the world due to this crisis.”

Insulate Britain said it was not involved with setting up the event, which began after more than 200 supporters of the imprisoned activists gathered outside the Royal Courts of Justice in the afternoon.

One campaigner, Gully, told the crowd: “Make no mistake, these are political prisoners and they will not be the last.”

15:14

The group then walked from the courts to Westminster, chanting “power to the people”.

Insulate Britain began a wave of protests in September and blocked the M25, other roads in London, Birmingham and Manchester, and near the port of Dover in Kent.

The nine protesters were sentenced at the high court on Wednesday after admitting breaching an injunction by taking part in a blockade of the M25 during the morning rush hour on 8 October.