A Nigerian passport holder must hold one of three visas to even land in the UK: which means individuals can "be" in the UK for up to 24 hours.
This allows them to connect to another flight within 24 hours as long as their bags are thru checked and they have been checked into their connecting flight.
In reality you're talking to a criminal sitting in a cybercafé with a well-rehearsed script he's used many times before.
He's hunting through chat rooms, dating sites and social networking sites searching for victims, looking to cash in on romance.
A check or money order is only a promise to pay or provide funds.