Hugh Grant has said he considered formally entering politics before the general election, but instead decided to campaign for people to vote tactically to prevent a Conservative majority to stop Brexit.

Speaking before he canvassed in Westminster with Chuka Umunna, who is standing there for the Liberal Democrats, the actor said he had decided his best role in the election was “banging the drum for tactical voting”.

Grant is also due to campaign on behalf of remain-minded Labour candidates, and said his “personal fantasy” for the election would be another hung parliament with MPs in charge.

Asked if he had considered standing himself, Grant said: “I wanted to help at this election and that was one idea that crossed my mind. But I think I would struggle to follow party orders. I think I might be too old and too pleased with myself to be obedient.”

In a brief speech alongside Umunna amid a crowd of Lib Dem activists, Grant said voters should “do everything we can” to stop a Conservative government.

“I don’t want to sound dramatic – even though you could argue that is my job – but I really think we are facing a national emergency,” he said. “I don’t think that what is left of the Conservative party, once they’ve expelled anyone who was responsible or decent or sane, is something I can contemplate as the government of a country that I love.”

Speaking to reporters afterwards, Grant said he feared “a Tory majority who will take us out of the EU and in an almost certainly chaotic fashion”.

He said: “Because like many I give no credence to the argument that one year will be enough to make a new free trade with the EU, and that therefore we will crash out at the end of 2020. And I want to do my modest bit to try and prevent that national catastrophe.”

Asked if he was surprised to find himself knocking on doors to canvass for a politician, Grant said: “I did used to sell fire extinguishers door-to-door. I was very good. I also sold coat hanger covers. They’re brilliant. I might go back to that, actually.”