Two British opposition parties want to hold elections even earlier than Prime Minister Boris Johnson has proposed as they try to ensure the country doesn't leave the European Union without an agreement.

The Scottish National Party and the Liberal Democrats say they will push for a December 9 election, three days earlier than Johnson has proposed and years earlier than the next scheduled vote in 2022.

They also plan to ask EU leaders to extend the Brexit deadline to at least January 31 to provide more time to debate Johnson's withdrawal agreement.

Johnson says if lawmakers approve a December 12 election he will attempt to push his Brexit deal through Parliament quickly. He is seeking to delay Britain's October 31 Brexit deadline by only a few weeks to keep pressure on lawmakers.