UniBoard, also family-owned, is based near Dublin and the deal means EBB will now have a presence in the Republic of Ireland.

EBB said it would become the largest stockist and distributor of cartonboard in the UK and Ireland as a result, holding more than 15,000 pallets of cartonboard and other packaging products in stock.

UniBoard was established 21 years ago and has grown to become Ireland’s largest paperboard supplier, offering a wide range of packaging and display boards. It had sales of €16m (£14.3m) last year and employs nine staff.

Owners Myles and Sharon Fitzpatrick will remain with the company. Myles Fitzpatrick said the deal would help the firm grow into new areas, and “bring the business to the next level”.

EBB managing director Matt Elliott praised the Fitzpatricks for building a “fantastic business” with “great staff, loyal customers and excellent mill partners”.

“Since we first met it was obvious that our business styles were similar; the need for high levels of local stock combined with great distribution, an experienced and reputable sales force, backed up by efficient administration,” he said.

“We believe that we can not only strengthen UniBoard’s position in their local market, but this move also opens the door to allow us introduce and develop the EBB product range into the Irish market.”

EBB sales and marketing director Chris Sandwell said that UniBoard had been a respected competitor in the Northern Irish market, which is how the firms got to know each other. He said that having an Irish base within the EU could eventually turn out to be a “side benefit” for EBB post-Brexit, but it had not been a driving factor in the deal.

EBB will celebrate its centenary in 2022. The Farnborough-headquartered firm has sales of £150m and employs 290 staff.