How many bailiffs can act on the same debt concurrently?

Many.

If all bailiffs, or agents, are acting together using the same enforcement power, then they can act jointly provided one agent holds an enforcement certificate.^[1]

A person without an enforcement certificate may only act in the physical presence of an agent with a certificate,^[2] and the bailiff may take other people onto the enforcement premises.^[3]

If a creditor applies for more than one enforcement power (e.g, a warrant or a writ, etc.) for the same debt, then that is an abuse of the courts’ process, and you can apply to strike out the additional enforcement power,^[4] together with your costs.^[5][6][7]

^{[1] Section 63(2) of the Tribunals Courts and Enforcement Act 2007
[2] Section 63(2)(c) of the Tribunals Courts and Enforcement Act 2007
[3] Paragraph 27(1) of Schedule 12 of the Tribunals Courts and Enforcement Act 2007
[4] Civil Procedure Rule 3.4
[5] Civil Procedure Rule 44.2
[6] Civil Procedure Rule 46.5
[7] Part 3.1 Practice Direction 46.5}