do I need to name my main suppliers to the bank

Yes, but usually only as dependency and not as a list of names

In almost all cases: yes, this is a question where the bank expects an answer, but first check carefully what exactly is being asked. Banks usually do not ask this to obtain a complete supplier list, but to assess concentration risk: is the company heavily dependent on one or a few suppliers, and what happens to business operations if they fall away. This is part of the client due diligence that banks are required to conduct under the Anti-Money Laundering and Countering the Financing of Terrorism Act. The question often appears in the same questionnaire as the question what is the origin of the company's assets, because both relate to the robustness and origin of the company's cash flows.

In practice, banks usually ask for a percentage: what share of procurement from the largest supplier or top three suppliers, and sometimes the country of establishment of those suppliers (relevant for sanctions and money laundering risk). Names of individual suppliers are rarely needed; a percentage and possibly the sector is usually sufficient. If you do not have that percentage clearly, then "no concentration above X% with any single supplier" is also a valid answer, provided it is accurate. Note: this is a different question from the average payment term to suppliers — which concerns payment behaviour, not dependency.

Where this comes from: client due diligence and the Business Register

The bank's obligation to ask such questions stems from the client due diligence under the Anti-Money Laundering and Countering the Financing of Terrorism Act; supplier concentration falls under the broader risk profile of the customer that the bank must establish. The basic data of the undertaking itself — legal form, establishment, directors — come from the Business Register under the Business Register Act 2007, but supplier information is not included there and must therefore be provided separately.