John Lewis Partnership has posted a 14.7% slide in half-year pre-tax profits to £81.9 million, citing "deep structural changes in the retail market".
The group, which also owns Waitrose, said its commitment to competitive pricing, increasing pay and investment held back profits in the six months to July 30.
Chairman Sir Charlie Mayfield said the results were not linked to the EU referendum result.
He said: "We have grown gross sales and market share across both Waitrose and John Lewis, but our profits are down. This reflects market conditions and, in particular, steps we are taking to adapt the partnership for the future. These are not as a consequence of the EU referendum result, which has had little quantifiable impact on sales so far.
"Instead there are far-reaching changes taking place in society, in retail and in the workplace, that have much greater implications."