I worked at Softwire full-time
The culture is based on giving the best possible experience for the employees, while also solving customer's problems. The engineers are either highly skilled or strive to be. The common problem seems to be "how do we clean the mess the previous contractors left us with" - and they tend to excel at that. Superb opportunities for growth: it's the company strategy to make its employees grow. The most important: the company will take care of you, ensure you're happy and that you feel there at home.
The projects can be nice... and not very nice. Sometimes you have to deal with ancient horrors. The pay is not the greatest you can get in London - but remember that you will be usually shielded from soul-crushing or failing projects.
Advice to Management
Do the thing you are doing - the company culture is great. Ensure the knowledge is being transferred on old projects. Expand the hiring pipeline and deal with the company's size.
I applied online. I interviewed at Softwire.
Initial application via a straightforward online application form. Initial brainteaser style phone interview as described by other reviewers. Softwire were very quick to respond at all stages of the application process (a maximum of two days delay probably). Onsite interview process was much longer than I was expecting and consisted of multiple pseudocode problem solving puzzles, an on computer test (reasoning puzzles and essays rather than coding) and an HR style interview.