Supermarket chain Lidl is to invest more than £30 million and create more than 500 jobs in Scotland, with the firm saying it is attracting a higher proportion of "lower to upper middle-class shoppers" to its outlets.

Figures show the percentage of "squeezed middle" shoppers buying products in the German budget chain rose from 25% in 2011 to 41% in 2012, according to data firm Nielsen.

Lidl, and fellow German firm Aldi, have reported a rise in sales is because it says families are struggling to cope with rising bills and food prices, and little or no increase in pay.

Lidl, which currently employs 1500 people in Scotland, has announced it expects to create the permanent posts at its nearly 90 Scottish outlets, including one that is being built in Kirkcaldy, Fife. The jobs include roles at its regional distribution centre in Livingston, West Lothian.

Lidl, which made its first foray into the UK in 1994, says customer numbers have grown by up to 20% since it launched a major brand campaign in Scotland at the beginning of the month.

Ross Millar, managing director of Lidl Scotland, said: "It's been a tough few years for everyone in Scotland, but Lidl has continued to grow. The fact we are now looking to extend our distribution centre and recruit over 500 permanent employees is not only a good sign for us, but is also great news. With 88 stores across Scotland and the 89th store currently 'in build' the vacancies will be available across the country."

Lidl's investment follows Tesco reporting a drop in sales.

One study has claimed nearly two thirds of people in the UK are supplementing their weekly shop at supermarkets such as Marks and Spencer, Waitrose and Booths by visiting budget chains.

The survey says customers are buying items such as tinned goods, fruit, vegetables and toiletries at so-called upmarket stores before going to budget supermarkets for items such as wine and champagne, according to website vouchercloud.com.

Of the 2000 people surveyed, 64% said they used "budget super-markets as well as upmarket stores". And of those who use upmarket and budget supermarkets at least once a month, more than two-thirds (68%) use budget supermarkets more often than they did a year ago.

Sixty nine per cent of survey respondents also said they use budget supermarkets more often than one year ago.

Lidl is continuing its marketing push at this weekend's Royal Highland Show in Edinburgh, where it will showcase Scottish products from shortbread to salmon and a range of whisky.

Alasdair Fowle, public relations manager for Lidl Scotland, added: "We were already seeing great growth figures in Scotland but since the branding campaign started – especially the television aspect of the campaign – our stores have seen a huge surge in customer numbers."