Plot hole: Tom and Anna assumed the £220,000 they found in the suspended ceiling belonged to their deceased tenant Ben (on disability and renting their basement), but it more reasonably could have been hidden there by the previous homeowner - Tom's grandmother. (Some people live frugally while hoarding cash.) If they inherited the house, they also could have believed they inherited the hidden cash, so did not have to worry about someone looking for the money or getting into trouble for keeping it. (00:14:30 - 00:15:15)
Plot hole: Tom told I.D. Halden, "My grandmother passed a few years ago and we inherited the family house." If there was a mortgage, who was paying it for a couple years? And if the house was inherited, there would not be a landlord, they would not be paying "rent", and owners do not get served with an eviction notice. (There was no mention of a legitimate reason, such as unpaid taxes.) There's a failure to discern home ownership (with a mortgage) from renting a house (which is not "inherited").
Suggested correction: It seems to be that it is about two different houses, the rented one they already live in, and the inherited one which is renovated.