Google prevents too many similar results returned in the serps this could be one of the factors here but its likely because you don't have enough links actually to the twitter account. Google can associate whats relevant to you and what's not... Now Google will be aware that the 10th result is not your tweeter account, Google is attempting to give users multiple choices as well a serps with a full page of you, and no other Scott Helme would crappy for everyone else.
This isn't to say it can't be done but simply linking from the top position to another site doesn't always have the desired effect othersite shoe-companyA.com links to shoe-companyB.com and so on and then you would have shoe-companyA > D in the results.
The problem here is your expecting your site to pass all the SEO heavenly the love when its more complex than that and Google will need a lot more to give you that position. Take celebs for example, they have tweeter links all over and followers is also a factor... well some believe.
Also Google has the ability to know what self-created content is, so if you've created many profiles all linking to your tweeter account you'd hope that this would bump it up, it helps but it won't be a major factor since it knows they are profile links. My advice, more followers and more on the page inner content links to your actual twitter account. People with top rankings twitter accounts will often have hundreds of links from real content on other sites, not profiles, not citations company links or about.me links etc. Guest blogging is considered one of the best methods of ranking a twitter account since most sites excellent sites don't allow site promotion within the article your written but will often allow a twitter author attachment.