how to apply moving load using BS code

Have a look at section TR.31.1 of the Technical Reference manual. You can

a) choose a vehicle whose parameters are built into the program like the AASHTO HS20 or HS15

or

b) define the parameters of that vehicle (load thru each wheel of an axle, spacing between axles, etc.)

Data for vehicles from the British standards is not built into the program. Hence, you will have to specify it using method (b).

Have a look at section TR.31.1 of the Technical Reference manual. You can

a) choose a vehicle whose parameters are built into the program like the AASHTO HS20 or HS15

or

b) define the parameters of that vehicle (load thru each wheel of an axle, spacing between axles, etc.)

Data for vehicles from the British standards is not built into the program. Hence, you will have to specify it using method (b).