The Peterlee-based company, which is part of the Saga Group, now boasts 13 enclosing and eight polywrap lines.

So far this year, it has bought a Sitma 950 and two Sitma 1050 polywrapping machines, six state-of-the-art BB700 envelope-inserting systems from Buhrs and six cutting and folding machines

Managing director Alan Purvis said: "This is our 20th anniversary year and it promises to be a massive one for us. Productivity is up by 25% and this improvement is down to continued investment in our people and plant.

"We've now increased our rate of collating and wrapping brochures to 70,000 an hour, so our productivity is set to increase yet again."

MetroMail claims to handle 45% of all business mail leaving the north, which involves packing, bagging and dispatching around 1m items each day.

The business is one of the biggest employers in East Durham with 220 staff.

Purvis said: "While equipment is important, we would not be successful without the people to run these machines being the best in the business. We owe an awful lot of gratitude to our staff who always embrace change and strive to be the best."

The company will now turn its investment eye to its printing side and has plans to replace its 12 laser printers towards the end of the year.