Can a withdrawal request result in the need for verification documents being requested?

Yes, financial transactions, such as deposits and withdrawals, can result in verification requests. Gambling Commission regulations that prohibit requesting verification documents due to a withdrawal do not apply when we have another clear legal obligation to request them. This is generally due to the value of transactions triggering a specific financial value that obligates us to make a request.

The law (here) explicitly states, as part of Regulation 27, that transactions that exceed 1,000 euros as occasional transactions and/or 2,000 euros in linked transactions require additional verification to be applied. We convert the euro value to the currency you play in. 

The regulations define the term ‘transaction’ to include both deposits and withdrawals. Therefore, withdrawals must be taken into account when conducting such transactional monitoring.

Gambling Commission advice: 

https://www.gamblingcommission.gov.uk/public-and-players/guide/age-and-id-verification