London, UK - Britain's top equity index fell on Tuesday, with sportswear retailer Sports Direct sliding sharply after its founder sold a chunk of shares in the company.

The blue-chip FTSE 100 index, which on Monday suffered its worst one-day fall in a month, dipped 0.3 percent, or 17.51 points, to 6,605.33 points in early session trading.

Sports Direct was the worst-performing FTSE 100 stock in percentage terms, falling by 6.4 percent to 836.17 pence after founder Mike Ashley sold 25 million shares.

A 4.1 percent fall at food and fashion conglomerate Associated British Foods (ABF) also weighed on the FTSE, with some traders attributing ABF's fall to a profit warning on Tuesday by German sugar producer Suedzucker.

According to Thomson Reuters StarMine data, Associated British Foods is on a price to earnings per share (P/E) ratio of 25.9 for the next 12 months - giving it a higher rating than similar P/E ratios of 12.7 for rival Tate & Lyle and 18.3 for France's Danone.

JNF Capital investment manager Ed Smyth said he believed ABF's rating was too high.

"We believe ABF is simply overvalued," he said.

The FTSE 100 rose 14.4 percent in 2013 to post its best annual gain since 2009 and it reached a peak of 6,867 points in January this year, near its best level since early 2000.

It has since slipped back amid a slump in emerging markets and tensions between Russia and Western powers over Ukraine.

Smyth said he felt the FTSE's broader upward trend remained intact, but Hantec Markets analyst Richard Perry was more circumspect.

Perry said the fact that the FTSE had fallen below its 50-day and 200-day simple moving average levels - often used by technical traders as a sign to sell on expectations of further weakness - pointed to few gains in the near-term.

"At the moment, the FTSE is coming under a little bit of pressure," he said.