Sales were up 11 per cent at £25.6 million in the six months to the end of May and pre-tax profits up from £1.45 million to £1.93 million.

The company has two divisions with its micro-filtration operation and its headquarters at Lynn.

Chief executive Ben Stocks said that Porvair is in its fifth year of increased sales and that the continuing growth is largely down to to the company's investment in research and development.

"We have been investing in new products for six years now and we can see the benefits for that.

"We also have half-a- dozen new lines which are beginning to generate sales."

He said that the company started the second half of the year with healthly order books in its core UK and US markets and is confident about the future.

"No-one is going to be immune to a strong global slowdown. We see no sign of that at the moment but we are watching it," he added.

Porvair employs about 500 people. split equally between Lynn and America. Although manufacturing in Lynn ended in 2003 it has kept its head office here.

"We have a long association with Lynn and we are very proud to be in the town," said Mr Stocks.