Store numbers rose by 36 to 465 in the year to March, while a further 11 stores will have opened by the end of August.
Retail director Peter Dodding said James Hall's focus on fresh food and its promotional and loyalty packages were key factors.
"We have a very strong commercial package to offer our retailers and have got off to a very good start this financial year," he said. "There will be a continued focus on recruiting new members throughout the year ahead. We get a lot of positive feedback on fresh foods and own label, particularly since our own-label offer was relaunched nationally."
He said many existing members were opening new sites and retailers were abandoning other symbol groups in favour of Spar.
One of the biggest draws for new members was the company's loyalty scheme, which paid out £1.1m to members in its first year of operation, ending in April.
A new sandwich factory was proving popular with retailers - with some retailers' sales doubling - and was already producing 60,000 sandwiches a week.