Ad-funded free digital music streaming service Spotify has temporarily reinstated its invite system in the U.K. due to "huge demand" since the mobile service launched on Sept. 7.

Spotify apps are available for mobile streaming for iPhones and iPod Touch devices as well as Android-powered phones for premium Spotify users who pay a monthly subscription.

The free service is invite-only in all other launch countries. The premium service for subscribers is available in the U.K., Sweden, France, Spain, Norway and Finland.

"We hope to be able to remove the need for an invite again very soon," said a Spotify statement. "Premium users will of course still get instant access as per usual and all current users will be able to use Spotify as normal."

The decision was taken to ensure that the increasing number of users did not affect the quality of the service.

"The invite system was put back on to ensure that the great user experience which we're known for doesn't suffer as we've been adding a lot of users (both free and premium) since we launched our mobile apps," explains a spokesperson.

The service has been fully open in the U.K. since February. Invites are available from existing users and those who sign up to the premium service.