Supermarket giant Tesco is to create 20,000 jobs in the UK over the next two years through "significant investment" in customer service, refreshing existing stores and opening new ones.

The firm said it will invest in additional staff hours and training and improve hundreds of stores.

It said it expects to focus on giving opportunities to young unemployed people.

The 20,000 jobs include full-time and part-time roles, including some apprenticeship placements. In addition, a number of existing staff we will invited to do apprenticeship placements as part of their current roles, but a spokeswoman could not say exactly how many people this was - or how many of the 20,000 jobs were full time or part time.

Tesco was targeted by Right to Work activists last month over the Government's work experience scheme, leading the retailer to offer to pay youngsters on the programme.

Prime Minister David Cameron said: "This is a massive confidence boost for the UK economy. Tesco is one of the world's leading companies and the biggest private sector employer in this country. Their commitment to creating jobs and opportunities for young people at what is a difficult time for the economy is fantastic news for the UK as a whole and for those people they will help into work."

Tesco chief executive Richard Brasher said: "In unprecedented economic conditions like these, major businesses have a big responsibility to step forward, invest and create jobs. Today's announcement is a huge shot in the arm for the UK economy.

"At the core of this investment is our determination to deliver the best shopping experience for our customers, bar none. We will invest in more staff on the sales floor at busy times, greater expertise and help in the crucial areas of fresh food, and enhanced quality and service across our stores at all times.

"To deliver this we're going to strengthen our customer service team: 20,000 more staff across our stores over the next two years."

Tesco is the country's largest private sector employer with over 290,000 staff, a quarter under the age of 25.

More than a million 16-24 year olds are unemployed.

The Government last week announced changes to its work experience scheme so that youngsters would not lose their benefits if they left early, following criticism of the sanctions attached to the programme.

Youngsters on the scheme are not paid wages but still receive their benefits.

Ministers say it has been a success, with around half those on work experience coming off benefits.

But the Right to Work campaign is continuing to hold protests against firms taking part, warning it will target restaurant chain McDonald's later this week.

Tesco's recruitment drive comes as it seeks to turn around its performance in the UK by increasing its levels of customer service, the standards of its stores and its pricing.

The supermarket giant saw nearly £5 billion wiped from its value in a single day recently after it revealed dire Christmas trading as a £500 million price cut campaign failed to bring in enough customers.

It has been losing market share in recent months as it is bruised by a price war with its rivals that has seen Sainsbury's introduce its Brand Match scheme and Asda to offer a guarantee to be 10% cheaper than rivals.

It reported a "disappointing" 2.3% decline in like-for-like sales excluding VAT and petrol in the six weeks to January 7, which came in below its own expectations.

It is thought that Tesco's campaign failed to strike a chord with customers because it is funded by a reduction in Clubcard points and one-off promotions.

As well as putting on more special offers to drum up sales, a key part of its strategy is take on more staff to improve customer service levels.