The Information Commissioner’s Office (ICO), which issued the fine, said the company had sent 2.5 million texts.

The messages were meant to encourage customers to use the ‘My EE’ app to manage their account and upgrade their phone.

EE said the texts were sent as service messages so were not covered by electronic marketing rules.

However, the ICO found the messages contained direct marketing and that the company sent them deliberately.

Andy White, director of investigations at the ICO, said:”These were marketing messages which promoted the company’s products and services. The direct marketing guidance is clear: if a message that contains customer service information also includes promotional material to buy extra products for services, it is no longer a service message and electronic marketing rules apply.

“EE Limited were aware of the law and should have known that they needed customers’ consent to send them in line with the direct marketing rules.

“Companies should be aware that texts and emails providing service information which also include a marketing or promotional element must comply with the relevant legislation or could face a fine up to £500,000.”

An EE spokesperson said: “We accept the ICO’s findings, and we’re working to improve our internal processes. We’re committed to ensuring our customers are fully aware of their options throughout the life of their contract, and we apologise to the customers who received these messages.”