While Tesco's march on the UK retail market may seem relentless, there is a host of factors that will eventually combine to halt the advance of the British supermarket leader.

But it won't be for a good while yet. Figures from research firm TNS show that Tesco's market share topped 30 per cent for the first time in the 12 weeks to June 19, up from 27.9 per cent just a year ago.

This is just the latest milestone in a process that has seen chief executive officer Terry Leahy's company double its sales since 2000, topple J Sainsbury from the top slot in 1997 and move into areas as diverse as insurance and contact lenses.

Tesco itself argues that the 30.2 per cent market share figure is misleading in that it excludes other retailers that sell food such as Marks & Spencer and Boots. But this also applies to the competition, and on the TNS headline measure Tesco is now virtually twice as large - and growing - as Asda or Sainsbury.

Inevitably, there has been a backlash, and the company's treatment of suppliers, competitors, staff and the environment have all come under the media microscope.

Campaign groups such as Friends of the Earth have lobbied strongly against the retail juggernaut, while the website tescopoly.org.uk has become home to myriad protesting voices.

There is little sign such opposition is affecting sales, however, where Tesco's razor-sharp focus on price, product availability and convenience seems to be winning hands down.

"There are usually natural reactions to this type of expansion; consumers get a bit tired or the competition gets a bit better," said analyst Nick Bubb of brokers Evolution.

"Tesco has been lucky in that the competition has been in disarray. But they'll eventually get their act together."

There are signs that this is already happening. Sainsbury chief executive officer Justin King can note with some satisfaction that his company's market-share slide seems to have halted, as the traditionally mid-market player puts a greater emphasis on low prices and product availability.