Western International Market
The Western International Market is a wholesale market in west London, England. One of the principal wholesale markets in the London region, it is located between Southall and Hayes, close to the M4 motorway and Heathrow Airport, and covers an area of 86 acres (350,000 m2).

The Western International Market is a wholesale market in west London, England. One of the principal wholesale markets in the London region, it is located between Southall and Hayes, close to the M4 motorway and Heathrow Airport, and covers an area of 86 acres (350,000 m2).
Check the official site before travelling; hours and prices can change.
More markets

Borough Market
London's defining food market — go early Saturday, eat your way around the perimeter.

Columbia Road Flower Market
Sunday-only flower market in the East End — 8 a.m. for choice, 2 p.m. for prices.

Maltby Street Market
Borough's smaller, scruffier sibling — railway arches, weekend only.
Source: wiki-list