A Labour source said: “We want to see lower taxes for working people, but we are too far away from a general election to start setting out tax policies.”

Ms Reeves told CityAm: “I think this speculation about Rishi Sunak cutting taxes, I think it is a sort of triumph of hope over reality.

“It’s all well and good to say the Chancellor believes in low taxes, but that doesn’t pay the bills, it doesn’t release money for investment. What does that is if you actually cut the taxes.” She stressed that politicians needed to be judged “by what they deliver”.

Ms Reeves also underlined Labour’s opposition to the 1.25 percentage point rise in National Insurance Contributions, which is set to come in next year.

Labour’s support of tax cuts comes ahead of the North Shropshire by-election on Thursday, in which the Conservatives face a reduction in their majority or the possible loss of the seat. Some bookmakers now consider the Liberal Democrats favourites to win the vote, sparked by the resignation of Owen Paterson.

When Mr Sunak delivered his budget last year he put Britain on course for its biggest tax burden since the 1950s, although the Chancellor stressed his “goal” was to cut taxes by the end of the Parliament.