if you're getting the first train at 5.30am, the website says you can check in up to 90 minutes beforehand, presumably 4.00am ... I can't find anything on the website that tells you whether the departure lounge is locked before that time, but even if it is there's plenty of places to hang around both in St Pancras and Kings Cross stations ... HOWEVER that area is not the most salubrious or safest of areas ... there used to be a big prostitution/drug dealing problem in that area ... with the coming of the Eurostar terminal I know the police for a few years now have been cleaning the area up and the problem is nothing like as bad as it used to be ... if you do decide to hang around there during the middle of the night you need to expect police and security to be questioning why you're there and possibly trying to move you on etc ... ALSO both stations are not exactly the warmest places to be hanging around so wrap up well
