Shares in Topps Tiles fell 2.7% in Wednesday morning trading after the retailer warned that its full-year profits would come in at the lower end of market expectations.
Prime minister Theresa May's announcement of a cap on energy bills sent Centrica to the top of the FTSE 100's biggest losers by close of trade on Wednesday.
Topps chief executive Matthew Williams said tougher market conditions had prevailed as the housing market slowed.
The parent company of British Gas saw its share price fall 6% to 179.30p.
Topps is listed on the FTSE 250 index, which was down 0.16% at 20,004.08.
Shares in rival SSE also sank, down 3.19% at £13.67.
At the same time, the blue-chip FTSE 100 was down 0.05% at 7,464.57, with Tesco falling 2.6%.
Tesco was also a major faller, with its shares down 3.2% at 183.95p despite rising second quarter sales and the resumption of dividend payments.
The supermarket chain announced a big rise in first-half pre-tax profit to £562m as sales rose for the seventh quarter in a row.
Advertising giant WPP led the blue chip index higher, up 2.86% at £14.03.
Tesco's shares were initially among the biggest risers on the FTSE 100 when the index opened, but as the morning progressed, it switched from being the index's top winner to being one of the worst losers.
Overall, the FTSE 100 closed marginally lower, down 0.01% at 7467.58.
The retailer's woes had a wider impact on the grocery sector, with rival Sainsbury's also down, shedding 1.8%.
The FTSE 250 finished 5.93 points down at 20,029.42
Energy firms were also hit as the government announced details of its much-heralded price cap on household gas and electricity bills.
On the currency markets, the pound rose 0.24% against the dollar to $1.3700 and edged up 0.11% against the euro to €1.12830.
Centrica was trading 4.9% lower, while SSE fell 2.2%.
On the currency markets, the pound rose 0.35% against the dollar to $1.3284 and edged up 0.09% against the euro to €1.1281.
