If a meeting is open to the public, anyone can come along.
In this particular case, I don't know the exact details of whether it's a public open meeting.
But I would guess a lot depends on available space and that one'd have to book beforehand.
Keith, you are a wee misinformed in your analysis of politics UK.
The majority of Tory grassroots members want an alliance with UKIP.
At the last GE, with 3.5% of the vote, UKIP is reckoned to have cost the Conservatives 20-40 seats in Parliament.
Now, at 15% of public support (among those of the electorate who would vote), how many more seats would that equate to?
Then you should consider that in some areas of Britain, UKIP has relatively low support, in others a very large support among the public. In these areas where they have a large following, they could either win seats, or prevent the Conservatives getting seats.
A proper analysis should be done free of personal party preferences and (mischief

), in order to give a credible view.
Believe me, Keith, the Conservatives are VERY concerned and worried about UKIP. And this is a fact, not party propaganda.