Diagonal hatching - this is used to separate lanes of traffic and to protect vehicles waiting to turn off the road. If the are is bordered by a broken white line you can enter it, but only if it necessary and safe to do so: if it is bounded by a solid white line then you must not enter it except in an emergency.
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/519129/know-your-traffic-signs.pdf
英国官方给出的路标和指示线的说明手册,你说的这种线的解释在第62页最下面
另一份简明易懂的补充
https://www.driving-test-success.com/road-lane-markings.htm
Diagonal hatching - this is used to separate lanes of traffic and to protect vehicles waiting to turn off the road. If the are is bordered by a broken white line you can enter it, but only if it necessary and safe to do so: if it is bounded by a solid white line then you must not enter it except in an emergency.