Your email is written as if you expect "number of people from the UK attending Wikimania" to be one of the metrics of the Chapter's success -
why
is this, out of interest?
I think it is self-evident that more people from the UK attending WIkimania would be a good thing. The chapter is in a position to help that. The WMF's sponsorship programme typically doesn't give many (or any) sponsorships to people in the UK, so it would be good if the chapter did instead.
Well of course we could decide that WMUK would pay the full costs of anyone from the UK who wanted to go to Wikimania. I'm not sure why that would be a good use of WMUK's funds, though.