GC22 - the new migration rules that replace MAC codes for broadband, simply do not apply to lines for customers with more than 10 people working for them or which are communications providers.
They suggest such migrations are best managed by a cease of old services and re-provide of new services with some overlap (and notable cost).
In some ways this is sensible, in some it is not.
They do not confirm who is responsible for determining that an end user has more than 10 people working for it, and who is liable if a telco acts on statements made by the customer on such things or what happens if number of staff changes over time.
They do not confirm the reason code to give when a losing ISP refuses a migration because its customer is more than 10 staff and hence "GC22 does not apply".
I have to feel that OFCOM have not thought this through.
P.S. - this is not just broadband, but fixed line telephone services as well!