JEREMY Corbyn will today offer the “biggest ever rail fares cut” south of the border in an attempt to further narrow Boris Johnson’s poll lead.

The Labour leader will promise a 33 per cent cut in regulated fares next month if he becomes Prime Minister, saving the average commuter in England £1097 a year.

The £1.5bn policy would be paid for from existing Department for Transport budgets and by ring-fencing money from the £6.5bn already raised by Vehicle Excise Duty.

Labour said it would set aside part of the revenue to create a “sustainable transport fund” and carry our road repairs, rather than build new roads adding to congestion and pollution.

Rail transport is devolved, but Labour suggested the cuts would apply to cross-border routes.

The party said: “Decisions on whether to fund rail fare reductions in Scotland and Wales are a matter for the devolved governments. This policy clears the way for Scotland and Wales to follow suit if they wish.

“In the meantime the fare reduction will apply to rail journeys wholly or partly within England.”

The Tories called it “desperate”.

If follows news that average fares will go up 2.7 per cent in January.

Although Labour’s manifesto said the party would nationalise rail and “save you money on fares”, it did not contain any specific figures.

The new policy would apply to regulated fares”, which account for around 45% of all fares, and include season tickets and peak time tickets.

Since 2010, regulated rail fares have risen around 40% in England, or more than twice the rate of wages.

The eye-catching giveaway, which follows last week’s £58bn offer to compensate 3m women who lost out on state pensions, comes as new polls showed a narrowing of the Tory lead.

Three of four polls yesterday showed Labour catching up.

Opinium said it had moved from 19 points to 15, YouGov from 11 to nine, and BMG from 13 points to six. However Savanta Comres found the Tory lead growing from 7 to 10 points.

A Tory lead below seven points would indicate a hung parliament.

Mr Corbyn said: “Travelling by train is my favourite way of getting around the country but for too long a fragmented and privatised rail system has ripped-off passengers. Taking back control of our railways is the only way to bring down fares and create a railway network that is fit for the future.”

Transport Secretary Grant Shapps said: “You simply cannot trust Corbyn to deliver what he claims. His ideological plans would wreck our economy, cost people their livelihoods and with the help of Nicola Sturgeon would waste the whole of next year on two more chaotic referendums.”