Daisy Howarth's flight was on the tarmac bound for Cuba when a tannoy announced that the runway was closed because of an emergency landing. Hear the account she gave to ITV London:
More top news
The assault took place after a woman got on the train from Oxford Circus station with three children aged between two and five.
The sex offender was reportedly transferred from HMP Wakefield in West Yorkshire to HMP Belmarsh, south-east London.
Officials say the lizard, about 30cm long, is believed to be a Bengal variety, but it is not known where the reptile's journey started.