LONDON, Jan 4 (Reuters) - The number of shoppers heading out to stores, malls and other outlets across Britain fell 23.3% last week from the week before, as the government tightened COVID-19 curbs, market researcher Springboard said on Monday. People in large parts of southern England entered the toughest level of restrictions in the week following Christmas, joining the 16 million already in Tier 4 where non-essential shops must stay closed. Shopper numbers, or footfall, was down 31.8% in shopping centres, down 21.9% in high streets and down 16.8% in retail parks in the week to Jan. 2, Springboard said. Footfall across the UK as a whole was 55.7% lower than in the same week last year, it added. “The end of the festive trading period and tightened government restrictions unsurprisingly saw footfall in UK retail destinations drop significantly at the end of 2020,” Springboard director Diane Wehrle said. “Moving into a new year, with the extension of Tier 4 across virtually all of England and lockdowns in place in the devolved nations, retailers are unlikely to see any respite until restrictions are eased in the coming weeks or months,” she added. (Reporting by James Davey, Editing by Paul Sandle and Andrew Heavens)