Believed to be the UK's oldest airline still operating under the original name.
No, that's British Airways, which has been operating under its original name since 1935. The ownership was transferred to BOAC in 1940, when the operating name was not used, but still owned by the legal department of BOAC, until 1974, when the original name they had always owned was brought back into use, and with the same shares having been current throughout.
Anyway, congratulations to Loganair for 50 years of being around, even if (like the BOAC period described above) the name doesn't appear as the main fleetname on the aircraft any more.