When Cassie Stuart uncovers evidence in an old BOAC bag, she says she remembers her brother having one in 1978 from Alicante airport. BOAC ceased to exist in 1974 (they became British Airways after merging with BEA). Also BOAC never flew to Alicante, so she could not have bought one there.
When DCI Cassie Stuart finds the ignition key, Kelly the forensic technician tells her that "the ignition key wasn't invented until 1949" and that the key must date from after this year. This is not true. Ignition keys had existed long before that, even though it was only in 1949 that Chrysler first combined the ignition switch with the starter-motor control.
The phone numbers shown in the diary from 1976 show the area code as 01946, these weren't amended until 1995, so would have been 0946.
The telephone numbers for the contacts in the diary found all begin '01', (e.g. 01946). The diary was from 1976, but UK telephone prefixes did not have the '1' added until 1995.
The car to which the key belongs has registration number 775 UCC and was registered in January 1966. However the format of registration numbers was changed in January 1963 to the ABC 123A format, where the isolated letter is a code for the year. Not all regions adopted this straight away and some cars still used the old system. However, this was made compulsory for all regions in January 1965. A brand-new car registered in 1966 should have a year-letter of C, to indicate a 1965/6 model (for example UCC 775 C) and not a pre-1963 registration number.