The log on the site front says No Report ... which often means severly delayed; that was the case this morning - I check the running about five minutes before the train is due, and it hadn't even left Swindon at that time ... but it did run later.   

I note that although it was 20 late off Swindon, the live departure boards are forecasting an arrival in Southampton within 5 minutes of schedule.   That shows just how 'slack' the timings are, and also means that the train will be recorded as being "on time" in the official statistics.

Other causes of "no report" ... a train that's cancelled but that's not been put on the system , but it can also simply mean that the monitoring system is down and the train ran to time.