The outlook for companies with operations focused on Britain's domestic economy is starting to look gloomier as firms begin to report earnings from the first full quarter following the U.K.'s vote to leave the European Union.

Travis Perkins (TPRKY) , a building materials supplier, has fallen 6.85% in London as the FTSE 100 lost 0.33% to sit at 6,977.11 after saying it will likely miss full-year earnings expectations. It's shares have lost 37% since the June 23 referendum.

Foxtons, Britan's dominating real estate agent group, said Wednesday that lower property sales in London have pushed sales revenue down by a third. Shares in the company have gained 3.17% today.

And this could be just the beginning with the divergence between the FTSE 100 and FTSE 250 becoming more important.

The fall in the pound, which has slid about 19% since the Brexit vote, has propped-up the internationally focused FTSE 100. Credit Suisse recently calculated that London's benchmark index's constituents collectively earn about three-quarters of their revenues from outside the U.K. The FTSE 100 is up 10% since the June 23 vote and is now hovering at record highs.

The domestically-focused FTSE 250 is, however, a different story, having only gained 3.44% since the referendum. Its constituents are exposed mainly to the British market, which three months on from the Brexit vote is now feeling the pinch. Market uncertainty has worsened since Prime Minister Theresa May looks to be favoring a "hard Brexit", or more simply, a divorce from the EU that does not allow the U.K. access to the single market.

Lack of access to a single market could prove to be a sticking point with these smaller FTSE 250 companies that trade with Europe.

Both Travis Perkins and Foxtons have expressed concern for their businesses since the referendum. Travis Perkins has said that it expects 2016 core earnings to be "slightly below" the current market consensus of £415 million ($509 million). It has decided to close more than 30 branches and make further efficiency changes in the supply chain.

The company said demand remained "softer" throughout August and September and remains "uncertain" going into next year.

Foxtons, on the other hand, said home buyers shying away from transactions in the wake of the Brexit vote due to higher property taxes will hit their bottom line. Quarterly sales revenue came in at £12.2 million pounds for the three months ending September 30, down from £18.5 million in the same time period last year.

It warned in June that the vote would lead to less transactions that would probably last until the end of the year. However, in its Wednesday statement the company said tight cost controls will help deliver full year results in line with expectations, prompting the boost to shares.

These warnings are expected to be just the beginning as inflation increases and consumer confidence falls. Data from IHS Markit released Wednesday show that U.K. households saw a noticeable downturn in their finances for the first time since the vote. A household finance index fell to 43.8 in October, a five-month low and down from a reading of 44.7 the previous month.