While some tubs are plated in porcelain, they are actually constructed of other materials. Fiberglass and cast-iron are the most common.
However bath tubs are not made of porcelain, but of porcelain enamel on a metal base, usually of cast iron. Porcelain enamel is a marketing term used in the US, and is not porcelain but vitreous enamel.
When Sam & Barry are trapped in the house, Sam tries to use the landline phone to dial out. When he picks up the receiver a "fast busy" signal sound is heard and Sam says "they cut the line". If the line was cut there would be no sound. The fast busy is indicative of trouble on the line, not a dead line.
Some of the dialogue between Sam and Barry, as they are hiding from the bad guys, echoes when it shouldn't.
Hartley is using a Sat (Satellite)Phone, not a cell phone. A Sat Phone is not dependent on cell towers, it uses satellites. It will work as easily in the middle of the Gobi Desert as it would in the middle of New York City..
When Sam can't get a cell signal to call for help, Barry tells Sam that he chose to hide records at the lake house because cell service was unavailable. However, a few minutes later, Garret Hartley is shown talking on his cell phone in the driveway and Sam says he's calling for backup. Almost immediately, Sam's escape plan fails and he says Garret's reinforcements showed up. Obviously, Garret was able to call out on his cell phone.
Fiona talks about the English government, instead of the British government. There is no such thing as the English government.