Waitrose online shopping partner Ocado claims to have cracked home shopping with 99% accuracy on delivery times and less than 2% substitution rates in trials.
Joint md Nigel Robertson said the service has achieved 25% penetration in Hertfordshire since a staggered roll out began in January "redefining the standards of online shopping."
He said: "Research tells us we are taking customers from Tesco and Sainsbury, as we roll out in bite sizes.
"We are very proud of our low substitution rates, they are less than 2%, compared to 15% to 20% combined with poor general availability at competitors."
And joint md Roger Whiteside said Ocado sends out fresher short-life products than competitors like Tesco.
He said nine out of 10 items delivered by Ocado are perishables like fresh produce, meat, fish and poultry. Unsold products are disposed of a day before they reach their sell-by date.
Ocado has just secured a second round of funding worth a total of Â£20m, Â£17.5m from Waitrose parent John Lewis Partnership and the balance from investment bank UBS.
Waitrose md Steve Esom said: "Ocado is a way for Waitrose to tackle home delivery and roll out the brand in unsaturated areas. It is dedicated to home delivery, and services a type of customer we can't reach through Waitrose Deliver."
Ocado extended its reach to 200,000 more postcodes in north London this week, bringing its total catchment area around Hemel Hempstead up to 1.2 million homes.
It is to roll out across the M25 region in the next few months, and will then be launched in Birmingham and Manchester.