as with any new stock to a rail line, all platforms, tunnels, over and underbridges along with overhead wire heights and signal structures need to be checked for clearances, just incase the train hits something and derails or causes a problem for following trains.
while scotsman has probably driven those lines before, things get moved, tracks slewed over etc, always best to ere on safety, wghen a train full of hundreds of people, many galons of boiling hot water and a huge weight are involved.
and as we speak new hitachi trains are also being checked for clearances on the ecml
http://www.rssb.co.uk/Library/groups-and-committees/2013-guide-vehicle-structure-sic-guide-to-british-gauging-t926.pdf
page 62