Research In Motion, the maker of BlackBerry smartphones, was battling to shore up its network on Wednesday as it emerged that an intermittent service outage preventing users accessing email had spread to 30m-40m people, half of all subscribers worldwide.

The three-day-old technical problems, which began at a datacentre in Slough outside London, were affecting users in the Americas, Europe, India, the Middle East and Africa – the biggest network failure to hit the Canadian company since it launched the BlackBerry service a decade ago.

Together with RIM’s slow and limited public response, the problems have outraged users who have had patchy or no BlackBerry email or messaging services since Monday morning. The incident has also raised questions about RIM’s oft-touted 99.999 per cent network reliability rating and could encourage both business customers and consumers to look elsewhere.