The stainless lines that came with my expensive Wilwood front brake kit, are
not marked DOT, however the AN3 Russell line I bought from Summit for my home engineered rear disc brakes is DOT marked.
Both have the stainless braid covered with plastic, which I understand is one of the DOT requirements.
The thread in the Girling lines is the same as AN3, so easy enough to buy that same Russell DOT approved line:
https://www.summitracing.com/parts/rus-r58362s
A common AN3 bulkhead connector at one end:
https://www.summitracing.com/parts/aaf-all50092 with
https://www.summitracing.com/parts/aer-fbm5556
The calliper end is not as straightforward. One could use a AN3 union with a copper crush washer at the calliper spot face.
https://www.summitracing.com/parts/vpe-10230
It seems from the pic that an AN union with a copper crush washer is the approach of one UK supplier:
https://forestcustom.co.uk/shop/brake-system/front-brake-hoses-stainless-braided?mfp=39-tiger[mk-i,mk-ia,mk-ii]
Thread engagement length is short with the AN union + copper washer method, and the AN nut is smaller than common crush washers. While it is being done, I would prefer a longer thread engagement length, and a larger nut to fully support the crush washer. Google tells me that the 37 degree AN flare is compatible with the Girling bubble flare seat in the calliper input, but I have yet to find supporting data. I am not aware of a long reach AN3 union in order to seal in the seat, or a "large nut" AN to use with the crush washer method.
I would buy the UK lines, but not plastic covered, and I have to get a provincial inspection so I "need" the DOT marking. It remains to be seen if using AN fittings, or bodged AN fittings, on brake systems will pass inspection.