I did not ask, as I was getting uk bank charges and I decided to close my account. They have a online form, if you search for gov.uk "International pension centre" you can ask them, they respond in one or two days, back by email or call them.
It's a question that you need to ask your local immigration office. I tried to do this and my local office reacted badly. In anyevent you will need 12 monthly transfers over 40kthb as a minimum.