The company is now in redundancy consultations with affected staff.
Latest results announced today for the first half of 2020 show HSS made a pre-tax loss of £12.9m compared to a £7.9m loss in the same period last year.
Turnover fell to £125.8m from £161.4m but revenues picked-up to 90% of 2019’s levels in September.
HSS shut its branch network at the start of lockdown and will now permanently close 134 of its 240 sites.
Steve Ashmore, Chief Executive Officer, said: “While our strategic ambitions remain unchanged, Covid-19 has demonstrated that we are now ready to accelerate our strategy by further investing in our technological platforms.
“These investments will allow us to reduce our physical footprint which, whilst regrettably resulting in the loss of around 300 roles, allows us to become a more agile, technology-driven business which is essential in our markets as well as reducing costs and enhancing shareholder value.
“This will build on our already differentiated commercial proposition and create the most advanced, customer-centric offer in an increasingly competitive marketplace.”