Entity to be registered: clubs and associations: independence of sections, branches, sub-clubs and committees - registration
If, having made all the necessary enquiries, you decide that the subsidiary entities are not independent of the parent organisation, you should advise the trader that tax on the activities of all the subsidiary entities and of the parent organisation must be accounted for under a single VAT registration.
If, on the other hand, you conclude that the subsidiary entities are independent, you will have to register each one of them appropriately.
However, you may wish to consider issuing a notice of direction under the VAT Act 1994, Schedule 1, 2 (artificial separation of business activities for VAT purposes). See VATDSAG for further details. (External users can find this guidance at http://www.hmrc.gov.uk/manuals/vatdsagmanual/index.htm).
In either case, having established whether there is one single entity or several, you will then have to ascertain what entity each one of them is, in accordance with this guidance, and register them appropriately.