Just thought I'd post a reminder that over the coming Bank Holiday weekend Euston Station will be completely closed for all but Underground traffic, meaning disruption not just for trains to Liverpool/Manchester/Glasgow, but also trains to Watford Junction for the Harry Potter tour.
If you're going to the tour at this time, you have a few options:
Jubilee line to Stanmore, where rail replacement buses and TfL bus 142 will operate to Watford Junction
TfL bus 258, which departs from Harrow & Wealdstone (Bakerloo), Harrow on the Hill (Metropolitan) and South Harrow (Piccadilly)
Metropolitan Line to Watford (this is a terminus on a spur, so be wary as not all Metropolitan line trains will terminate there) and a taxi from there to the tour. As I understand it local taxi firms are laying on extra cars in anticipation.
Regardless of route, be prepared for a longer journey and big crowds, not helped by the fact that Watford FC are at home on Saturday as well.