I note that most uses of the name on their website are given as 'one',
in single quotes, which at least makes a clear distinction from the
pronoun or number one. The National Express Group press release has
'One' at the beginning of sentences, but the website has lower case
throughout, so they haven't got consistent standards for their own brand
yet.

Especially as it is an abbreviation for Operated by National Express, so
maybe it should be ONE or, even worse O.N.E. (does anyone put the dots in
any more?)
--
To reply direct, remove NOSPAM and replace with railwaysonline
For Railway Information, News & Photos check out the Award Winning Railways
Online at http://www.railwaysonline.co.uk
"Loving First Great Western Link since 2004"