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* FTSE 100 down 0.4 pct
* Shares in oil producers, miners weigh
* Aston Martin plans IPO
By Kit Rees
LONDON, Aug 29 (Reuters) - The UK's top share index dipped on Wednesday, weighed down by commodities-related stocks as optimism over progress in global trade relationships has largely fizzled out.
The blue chip FTSE 100 .FTSE index was down 0.4 percent at 7,587.75 points terms by 0900 GMT.
The FTSE index underperformed broadly flat European equity markets, as sentiment turned cautious.
While investors have been optimistic over a proposed trade deal between the United States and Mexico, questions remain over whether Canada will also agree to the revised trade terms. looming deadline on U.S. tariffs with China also kept markets on edge.
"There is still a little optimism doing the rounds in light of the US-Mexico trade deal, but investors haven't been given another reason to buy into the market," David Madden, market analyst at CMC Markets UK, said.
Shares in UK-listed oil and gas firms took the most points off the index, with BP BP.L and Royal Dutch Shell RDSa.L down 0.6 percent and 1.2 percent respectively as the price of oil slid.
Shares in mining companies were also on the backfoot as worries over Chinese demand and a stronger dollar hit the price of London copper. MET/L
Glencore GLEN.L , Rio Tinto RIO.L BHP Billiton BLT.L and Anglo American AAL.L all retreated between 0.5 to 1.5 percent.
Big consumer stocks also added to the pressure on the index. British American Tobacco BATS.L and Diageo DGE.L were down 0.9 percent and 0.2 percent respectively.
Among outstanding movers, shares in Bunzl BNZL.L rose 3.5 percent and were the biggest gainers.
The business supplies distributor reported first-half earnings in the previous session and saw its shares close slightly lower, so Wednesday's bounce was somewhat of a recovery as investors digested Bunzl's results.
The UK's mid cap index .FTMC was also subdued, trading 0.1 percent lower. Nerves over the possibility of a 'no-deal' Brexit have contributed to a lacklustre performance for UK equities, with the FTSE 250 up just 0.6 percent this year, while the FTSE 100 is down 1.2 percent.
This is compared with a 0.3 percent decline for euro zone stocks .STOXXE .
In a sign of confidence, however, luxury carmaker Aston Martin set out plans to float on the London Stock Exchange, hoping to complete the flotation this year. brand strength is unquestionable but at the end of the day some investors will only want to get involved if the business can sell more units than it did in the previous year and at a higher price, and continue this trend ad infinitum," said Russ Mould, investment director at AJ Bell.