What is published in the LoA's between London TCC and Brussels ACC is this:
Flights on L179:
Flights with destination EBOS, EBBR TMA (EBBR, EBMB, EBAW, EBCV) and EBCI may be accepted via L179. FL170 will be the maximum level. An approval request is required for traffic above FL115.
I'm not sure who is responsible for the information published in the RAD within Belgocontrol. Maybe you can use the contacts on the Eurocontrol RAD site:
http://www.cfmu.eurocontrol.int/rad/contact.htm