It's not so simple. These are the general issue Diplomatic plates. Your photo, 149 is from Ethiopia.But, most embassies are awarded 1 special plate (sometimes 2, like Netherlands for example), usually used by the Ambassador (but not always) referencing the country they are from. So 149 Ethiopia also has 1 EE .Russia for example has 1 RF .But not all follow normal GB rules, for example, Qatar has QTR 1 with the letter Q in the sequence. The best in my opinion is Spain - SPA 1N .You may also be interested to know the Soviet Union was allocated 1 SU , but it was cancelled, and has not been released for private sale (blocked).