The move will see a dedicated area built specifically for storing dry goods which range from pasta and flour to items such as cooking oil and orange juice.
At the moment those are stored at various parts of the family-owned meat and fish supplier's main premises close to Linlithgow, West Lothian.
The work, which is to be completed before Christmas, will also result in increased floorspace for chilled food storage and additional processing capacity as the areas where the dry goods are currently stored can be easily adapted for other purposes.
Managing director Christopher Campbell said: "It is an extension for our dry goods as part of the continued expansion of the factory. We actually have dry goods stored in chilled areas or areas which could be chilled.
"So we are moving them out of the chilled area into a dedicated extension specifically for storing goods which don't need to be chilled.
"That frees up a lot of space in the factory for us to use in chilled storage and production."
The work is likely to be funded from the company's funds and cashflow. It paid off its bank loan in 2013 and has not sought any additional external funding.
The business, which supplies to top chefs such as Nick Nairn and Martin Wishart, saw turnover increase nine per cent in 2013, to £55.2 million from £50.7m in the preceding year.
Pre-tax profits doubled during the year to £1.63m from £828,000.
Mr Campbell, who has been running the company for more than eight years after taking over from his father Edward, said the extension would likely result in "four or five" new jobs being created.
The workforce at the moment is close to 320.
Campbells moved to the Linlithgow site, a former abattoir, in 2009 after a fire caused by a gas leak destroyed its factory in Broxburn.
The company also supplies products to hotels and food service outlets.
It has a supply agreement with Aldi for a number of fish, including pollack and cod, which are landed at Scrabster as well as salmon from Stornoway and Orkney.
Mr Campbell worked internationally as an accountant with KPMG before joining the family concern.