According to their website, trainline.com is owned by trainline holdings, which is owned by Virgin Group (80.5%), National Express Coaches (14%) and Stagecoach Holdings (5.5%).
Companies House have Trainline Holdings and Trainline.com listed at 120 Campden Hill Road, London, W8 7AR, each with their own Company Number.
A search on 192.com for Trainline, found this entry
http://www.192.com/search/search.cfmwhich will show you trainline.com but at a different london address, but with a geographical number. Might be worth a try?
Interestingly, although it shows Trainline.com with a Leicester Square address, if you click on that link it shows you Campden Hill Road address!