Oxford East MP Andrew Smith has warned that Labour MPs were prepared to block plans to hike car tax on polluting vehicles up to seven years old.

Mr Smith told the Oxford Mail he was willing to vote against changes coming in next April, which could lead to motorists being charged up to £455 in vehicle excise duty for cars registered as long ago as 2001.

On Wednesday, the MP refused to vote for a Tory amendment to the Finance Bill because it would not have guaranteed changes to the tax. Instead, he vowed to lobby ministers to ensure the variable tax applied to new cars only. Mr Smith said: "I am absolutely determined this has to be changed and they are going to change it."

The Conservative amendment, defeated by 63 votes, was backed by Banbury MP Tony Baldry, Henley MP John Howell and Oxford West MP Evan Harris. Witney MP David Cameron and Ed Vaizey missed the vote as they were out of London.