Mark-R
Member
Did wonder if that was the case but this government article and this page seems to suggest you can.
"They will consist of a green flash on the left-hand side of the plate and can be combined with the Union flag and national identifiers already permitted by the regulations"
The 2020 regulations that introduced the green plates seem to allow for letters and flags to be included with the green flash:
(4D) Subject to paragraphs (5) to (8) there may be displayed on a plate or other device referred to in (4A) an arrangement of letters corresponding with one of the sub-paragraphs of paragraph (9) and an emblem corresponding with one of the sub-paragraphs of paragraph (10).
This refers to paragraphs 9 and 10 from the original regulations:
(9) The arrangements of letters referred to in paragraph (4) are—
(a) “United Kingdom” or “UNITED KINGDOM”;
(b) “UK”;
(c) “Great Britain” or “GREAT BRITAIN”;
(d) “GB”;
(e) “England” or “ENGLAND”;
(f) “Eng” or “ENG”;
(g) “Scotland” or “SCOTLAND”;
(h) “Sco” or “SCO”;
(i) “Wales” or “WALES”;
(j) “Cymru” or “CYMRU”;
(k) “Cym” or “CYM”.
(10) The emblems referred to in paragraph (4) are—
(a) an image of the Union flag;
(b) an image of the Cross of Saint George, as depicted on the flag of England;
(c) an image of the Cross of Saint Andrew (the Saltire), as depicted on the flag of Scotland;
(d) an image of the Red Dragon of Wales, as depicted on the flag of Wales.
So a flash on the left with a green background can (I think) include a Union flag and the letters GB underneath and this arrangement should (I think) avoid the need for a separate GB sticker in most of Europe (but not Spain, Cyprus or Malta).