How much does a link-builder/content writer for an SEO company make on average in the UK?

[Jake]

I am not sure that there is an union or formal organization for such workers that would have such stats. The earnings of people in other countries is worth knowing, in particular you are subject to being replaced by outsources in 3rd world countries if you priced yourself too high.

Certainly native English writers demand a higher wage than some who generate 3rd rate search engine bait. Continuing your education in SEO technology and copywriting would put you in line for better paying positions, if not in SEO, perhaps writing sales page copy, which is quite lucrative for leaders in the field.

You can view the bids on projects similar to your work on freelance marketplaces like Odesk.com or Elance.com some freelancers using an article template and text to speech software can knock out articles quite quickly.

The Elance employment report which breaks down the jobs and worker locations in graphs, details how $60,000,000 was earned by Elance workers in the 1st quarter of 2013.
https://www.elance.com/q/online-employment-report