Waitrose has experienced serious speed and navigational problems on its new £10 million website, leading angry customers to complain on the supermarket's web forum and forcing the chain to apologise to customers.

The Waitrose.com website, which was launched two weeks ago, also caused loyalty codes to fail when users edited their baskets, and prevented users from entering long names as usernames.

The site was part of a revamp of the firm's online operation intended to make ordering easier, offer new services and boost sales. Waitrose managing director Mark Price said before the launch that it would "dramatically enhance the customer experience" so that shoppers receive "unrivalled standards of service".

However, after the launch led to major problems, users complained on online forums about the performance of the site, and Waitrose issued an apology.

"Please accept our sincerest apologies for the problems you have experienced with the new website and thank you all for your feedback," it said.

One user, 'Sea_the_stars', wrote: "After two hours, I don't know what I have ordered and what I haven't. I pasted my list into Tesco's shopping list and completed the order in less than 15 mins and 10% cheaper than Waitrose including their delivery charge. So it's goodbye from me!"

'PatsyPage' wrote: "I just can't find the things I want even after repeated searches but it's there if I scroll through pages and pages of listings. Some chosen items just never load up to my trolley despite repeated attempts and the whole thing seems slow, confused and frankly very cumbersome from a customer point of view!"

As a "matter of urgency" the supermarket said it was "still addressing" the overall speed of the website. Waitrose said it had "engaged our technology partners from around the world to help find a speedy solution".

Waitrose has not confirmed which technology was affected. It uses the Day Software CQ5 web content management platform from Adobe, but said it did not believe "at this stage" that the system was at fault. Adobe has not yet responded to inquiries.

The chain has made a number of modifications this week to rectify the issues, including changing login procedures, online basket filling systems and loyalty code recognition.

A spokesperson said login and ordering changes would go live “soon”, adding that as with “all new websites” there are “some problems”.

Leo King contributed to this report