There's a small piece about it in Steam Railway No. 525.
It was filmed at Darlton Quarry near Stoney Middleton in the Derbyshire Peak District, the filming taking place on 25 August. It was a diesel-powered 'Britannia' look-alike dressed-up to look Continental and allegedly 'no serviceable parts were harmed in the stunt'. The 'locomotive' had been previously tested on the GCR and NYMR.
Filming was originally intended to take place in Switzerland but the Swiss refused to allow the use of pyrotechnics, then using a 1908-built railway bridge in Poland but local authorities campaigned against it as it result in the destruction of sections of the bridge. A fake section of bridge was then constructed at the eventual location.