MK2 helmet flash help needed.

[NCA]

Heres my latest British mk2 helmet.RoCo 1940 dated, liner 1939 TTC marked.The colour is a slightly gritty Khaki/brown colour.

The flash has me stumped though!Some kind of Home Guard battalion?Army?...Thanks for looking.Flash is a blue cross on a yellow backround.

[Jerry B]

21st army group GHQ troops for attached Royal Artillery troops, presumably 51st or 5/1st. You need to google them 21st army group and see which arty units were attached to them. Also used by 21st army L of C troops which again might include arty. Either way it would be very early post war I think.

[NCA]

Thanks for your help.I did wonder if it was Royal Artillery...More research beckons!