Retail bellwether Marks & Spencer launched its seasonal Sale today, a fortnight earlier than last year.

The promotion comes as retailers across the board offer eye-catching deals to shoppers reluctant to spend as their disposable income is squeezed and the economic outlook remains cloudy.

Retailers including Debenhams and House of Fraser launched their summer Sales earlier this month, each a week earlier than in 2010, in an explicit attempt to bag share of spend at the start of the Sale season.

As stores chase sales and well-known retailers collapse, research released by PwC showed that last week, 70% of high street stores were on Sale or displaying promotions such as three-for-two in their windows. That compares with 60% last summer and 40% in 2009.

A Marks & Spencer spokeswoman said its decision was prompted by shopper behaviour as consumers hold on for bargains amid febrile trading conditions.

She said: “We looked at the market. It’s what our customers expect.”