The UK’s biggest online pharmacy, Pharmacy2U, has left patients without essential medication for weeks as it struggles with technical problems at a new warehouse facility.

The Daily Mail reported last week that some patients have been waiting four weeks for urgently needed medication.

Pharmacy2U says the problem has been caused by transferring its prescription dispensing service to a new automated facility, leading to “unexpected delays for some orders”.

Managing director of the Leeds-based company, Daniel Lee, said: “We are working closely with NHS England and the General Pharmaceutical Council to help patients who are affected.”

A message on the company’s website says that it may not be fully operational until 11 January.

NHS England has reportedly said the chaos caused is “not good enough” and the company needs to “raise its game”.

Pharmacy2U, an NHS-approved service, also hit the headlines last year when it was fined £130,000 by the Information Commissioner’s Office after information from more than 20,000 patients who used the service were offered for sale.

Emis Health has a 20% stake in the company.

A spokesperson for Emis Group said this was an operational issue for Pharmacy2U.

“We are aware that Pharmacy2U is rightly taking urgent steps to minimise the impact on patients caused by this issue,” the spokesperson said.