Labour and Conservatives have clashed over tax and spending plans as pre-election campaigning is stepped up.

Tory leader David Cameron called Labour claims of a £34bn funding gap in his party's policy commitments "junk" as he trailed his party's health plans.

But he was forced on to the defensive over tax breaks for married couples after telling the BBC he hoped to bring them in but could not promise them.

Mr Cameron later issued a statement saying they would "definitely" come in.

Lib Dem leader Nick Clegg said the two parties were "increasingly alike".

A man has been arrested after an 11-year-old girl was seriously sexually assaulted in a park in south Wales, police have said.

The 19-year-old from Pontypridd is being questioned in custody after his arrest in connection with the incident.

Police appealed for information about anyone seen acting suspiciously around Llanbradach Park, near Caerphilly.

The area was cordoned off and house-to-house inquiries have been carried out after the girl was assaulted near the village library at about midday on Monday.

Detective Superintendent Geoff Ronayne, who is leading the investigation for Gwent Police, said: "The young girl and her family are currently being supported by specialist officers following this horrific incident.

The freezing weather has raised fears that Britain could run short of gas after the National Grid issued only its second warning ever over surging consumption.

Demand for gas – the fuel used to heat about two thirds of Britain's homes – has risen to about 30 per cent above seasonal norms with Britain in the grip of one of its coldest winters for 100 years.

While it is unlikely that households will find their supplies restricted, a shortage could lead to higher bills.

The National Grid, responsible for meeting the country's energy requirements, issued a gas balancing alert on Monday to give warning that any further falls in supply could force big users like power plants to cut their consumption.

John Lewis said it had notched up more than half a billion pounds in sales across its department stores after a record-breaking festive season. Skip related content Related photos / videos Sales at John Lewis break record .

The group saw comparable sales soar by 12.7% year-on-year to £500.76 million in the five weeks to January 2 thanks to "excellent" Christmas and clearance trading.

Its resurgent supermarket chain Waitrose also hailed a strong Christmas, with total sales up 16.1% in the 13 weeks to December 26. Like-for-like sales rose 9% at the group's grocery arm - a performance which has thrown down the gauntlet to rivals ahead of Christmas trading updates from Sainsbury's and Marks and Spencer later this week.