B roadss are numbered routes in Great Britain of lesser importance than A roadss. See the article Great Britain road numbering scheme for the rationale behind the numbers allocated.

3 digits

B4000 to B4099

B4100 to B4199

B4200 to B4299

B4300 to B4399

B4400 to B4499

B4500 to B4599

B4600 to B4801

References