Depends on what you are looking for but Camden Market, Portabello Market are great and have original items.
For more mainstream there are the usual high street stores - try Oxford Street/Regent Street for Top Shop etc. Westfields is a large shopping mall out near Shepherds Bush Green or head to one of the outlet malls at Hatfield or Bicester, but these are outside of London.
What are you looking to buy? about 6 years ago
Top brands from Zara, Gap, H&M, Esprit, Next, French Connection, Top shop and other clothes shops can be found on Oxford street (www.oxfordstreet.co.uk ), Regent street (www.regentstreetonline.com ) and Carnaby Street (www.carnaby.co.uk).
Primark (www.primark.co.uk), selling affordable clothes, can be also found on Oxford street.
For "young fashion", vintage, hand-made clothes etc. I would recommend Spitalfields Market and Brick Lane (Sunday, close to tube station: Liverpool Street Station, more info on: www.oldspitalfieldsmarket.com). Portobello market (Saturday, Nothing Hill) and Camden Market are also good places for shopping.
For "Haute Couture" go to Harrods (www.harrods.com) or Harvey Nichols (www.harveynichols.com).
More shopping? :) Go to Westfield shopping centre (one is close to Shepperds Bush tube station, uk.westfield.com/london / second is close to Stratford tube station, uk.westfield.com/stratfordcity).
More info on London markets. Check London markets guide here: http://www.mintytrips.co.uk/london_markets_guide.html
Jacob about 6 years ago