I've added my suggestion to the meta page at http://meta.wikimedia.org/wiki/Wikimedia_UK_v2.0/Objectives:

"The charity's objects are the promotion of education for all through assisting the vision and mission of the Wikimedia Foundation: Creating a world in which every single human being can freely share in the sum of all knowledge by empowering and engaging people to collect, develop and effectively disseminate educational content under a free license or in the public domain"

Might need a bit of work in terms of getting it to flow.

It's very easy for us to explain how this is exclusively charitable and for the public benefit ("promotion of education" and "for all") and hence keep the Charity Commission happy. It's expressed in a way that keeps our autonomy so we are not controlled by a foreign organisation not registered with the UK Charity Commission.

By explicitly referring to the vision of the WMF, we comply with ChapCom's http://meta.wikimedia.org/wiki/Requirements_for_future_chapters which state "The mission of the organisation must be in line with the mission of the Wikimedia Foundation"

This leaves everything flexible, so projects that WMUK may come up with in, say, 10 years time, would not require us to rewrite the M&As.

The details of what we're actually planning to do - wikimania, schools etc. shoudl also be discussed and agreed (I suggest at the AGM in January) but I suggest we leave the Mem&Arts objectives broad.
Andrew