LONDON (Reuters) - Thorntons, the 110-year-old British chocolatier and retailer, said on Monday it would permanently close all 61 UK stores, putting 603 jobs at risk, blaming the impact of COVID-19 lockdown restrictions. Multiple lockdowns in Britain have heaped pressure on store-based retailers already struggling with tight margins and intense competition from purely online players. Thorntons, which was acquired by Italian group Ferrero in 2015 for 112 million pounds ($156 million) said the challenges it faced to trading were “too severe” and it would enter a consultation with impacted staff. “(The) changing dynamics of the high street, shifting customer behaviour to online, the ongoing impact of COVID-19 and the numerous lockdown restrictions over the last year ... has meant we have been trading in the most challenging circumstances,” said retail director Adam Goddard. He said Thorntons’ strategy going forward would be to focus on its online channel, where net sales had increased 71% over the last year, and on selling through grocery retailers. The group retains factories in Alfreton, central England, and Greenford, west London. ($1 = 0.7203 pounds)