A “foreign government” could have been behind a “seriously big” cyber attack which left residents unable to use the Southwark Council website over the Christmas and New Year period, councillors heard.

The distributed denial of service attack was “deliberately” carried out over weekends when the site has high volumes of traffic, Michael Scorer, strategic director of housing and modernisation, explained.

Speaking at an overview and scrutiny committee, he said: “At this stage there is a possibility they [the attacks] were from foreign governments.

“It was a seriously big attack. It was carried out very deliberately we think at weekends where we have higher traffic.”

The attack was like “banging on the door” but there wasn’t a data breach, cabinet member for housing management and modernisation, Cllr Stephanie Cryan said.

“There was no breach at all. It was literally just as if someone was knocking on the door, [but it] didn’t get though to any of our systems. It basically just disabled it for anybody trying to use the council website, which is a really disruptive tactic,” she explained.

The council did not know who was behind the attack and what their motivation might be.

“We don’t know who it was [and] you can’t trace who it is and we don’t know why they did it [or] will they do it to us [again] and could they then do something bigger? Is it someone who was really disgruntled with the service? We don’t know where it came from,” she said.

Ms Cryan said council staff responded to the attack immediately and that the council would never be immune from cyber attacks.

“It is one of those things, you are never not going to be immune to attacks and you are never going to stop them, but it is actually how you react to them and how you have those contingencies in place,” she said.

Ms Cryan said the council had contingency plans in place in the event of another attack.