But does anyone have access to how many people are employed in these digital firms and where they are located? This article suggests that there are hotspots in London, south-east England, Manchester, Middlesbrough & Aberdeen. But is there more detail?
The original article from the National Institute of Economic and Social Research (there's also a direct link to the PDF) has more detail on the geographic distribution of UK technology firms in the form of hotspot maps by Travel to Work Area. This is among a lot of other well presented information including breakdown of technology firms by sector, and growth rates of the "digital economy".
I suspect the articles you cite in your question did not look beyond the summary of key findings. Always look to the original published report as a primary source.