Primark, the clothing retailer known by its original trading name, Penney's In Ireland - and whose headquarters is still based in Dublin, has seen its sales growth slow significantly at existing stores, as it prepares to open its first US store in Boston later this week.

According to the latest accounts of its owner, Primark’s overall revenues grew by 13% last year, down from 22% just two years previously. Sales at like-for-like stores, when new openings are excluded, rose by just 1% last year.

Primark, which currently operates more than 280 stores across continental Europe, the UK and Ireland, is still very profitable and delivered £662m in profits for its parent company, Associated British Foods, last year – a doubling of profits over the past three years.

Associated British Foods has warned that the groups bottomline could be hit by strong pound and dollar values.

Primark is due to open a 70,000sq foot outlet on the site of the old Filenes Department Store in Boston, on Thursday, followed by a bigger store at the King of Prussia Mall outside Philadelphia, the biggest shopping centre on the east coast of the US.