The source requirements for the testing report of the UK PLUG BS standard ?

Overseas sellers want to sell British plug products.

According to The Plugs and Sockets etc. (Safety) Regulations 1994, there are the following British standards:

1) BS 1363;

2) BS 546;

3) BS 4573;

4) BS 5733.

The above four British standards, Which type of laboratory should be chosen to conduct British standard testing on products? What are the different requirements for laboratory qualifications in different British standards?

Thank you very much for taking the time to help me solve the problem.

Have a nice day.

Sincerely,

0toone