Revealing mistake: The 'earthquake' that takes place in this episode results in CGI-created cracks in the pavement that are very unconvincing. They do not appear to displace anything and - in a related continuity error - the cracks disappear in shots taken from ground level (the cracks are only visible in high-level 'looking down' shots).
Factual error: Emergency Service vehicles in Cardiff (indeed, throughout Wales) have their signs in bilingual English/Welsh. So the police cars and ambulances seen in this episode should have 'Heddlu'/'Police' and 'Ambwlance'/'Ambulance' bilingual logos. However, all the police cars and ambulances seen in this episode have their logos in English only.