PSN is back online after an unannounced server maintenance which happened earlier. The outage involves players having difficulty in accessing online multiplayer games, applications, and other online features. Although the network is currently back online for most regions, some UK players are still experiencing difficulty in accessing games like Fortnight and Rocket League according to the latest update from Express UK. Sony states that they are currently working on the issue and that it may be resolved within the day.
“Our engineers are working to resolve the issue as soon as possible, and we thank you for your patience.” - Sony PlayStation Support Team
Fortnight support team has also stated that the issue is not with the game but is largely connected to PSN's server outage. As of writing, PlayStation Network Status shows that all services for the UK are up running. Stay tuned for more gaming news and updates.
Source: Express.co.UK, PlayStation Network Status