A new report says that increasing use of search engine optimisation (SEO) by enterprises has led to the SEO market for the UK achieving a value of more than £500 million each year.

The report, by independent research company Econsultancy, says that the current market value represents a considerable increase over 2010 when the market was worth £436 million.

SEO is a specialist marketing device which involves the expert placing of key words and phrases discreetly within corporate websites to increase the chances of the latter appearing prominently on search engine results pages.

In assessing the market value of SEO, Econsultancy has not only included in its calculations the amount paid by businesses to SEO agencies, but has also added in the salaries and other payments that companies have made to their own hired SEO experts and administrators.

The report advises however that SEO is being played out against a rapidly shifting set of market conditions, all of which are providing increased opportunities for marketers, but which are in turn adding to the complexity of the discipline.

Among the developments cited by the report as having a bearing on SEO activity, is the increasing influence of social media, particularly given that search engine giant Google now also promotes its own Google + social networking site.

Another change to be aware of according to the report is the growing use of mobile devices for online activity. Search engine results pages, the report warns, are not read by mobile users in the same way as they are on PCs and laptops.