What happens to the #dropthebill hashtag when the PM mentions his NHS reforms?

As every political geek will know midday on Wednesday when Parliament is in session is Prime Minister's Questions. This week Labour Opposition Leader Ed Miliband led on the NHS reforms and how did twitter react? As you can see the Prime Minister's answers weren't convincing for his opponents on Twitter as there was huge spike in the  use of the #dropthebill hashtag. Interestingly the effect lasted after PMQ's has finished.

>require(twitteR)
> tweets = searchTwitter("#dropthebill", n=1500)
> length(tweets)
[1] 1499
> library(plyr)
> tweets.df = ldply(tweets, function(t) t$toDataFrame() )
> names(tweets.df)
 [1] "text" "favorited" "replyToSN" "created" [5] "truncated" "replyToSID" "id" "replyToUID" [9] "statusSource" "screenName"
 > range(tweets.df$created) [1] "2012-02-22 08:09:59 UTC" "2012-02-22 16:28:16 UTC"
> require(ggplot2)
> qplot(tweets.df$created, data=tweets.df, geom="histogram", main="#dropthebill on 22nd February 2012", xlab="Time", binwidth=1200)