Justdamo:
So just to be clear, I can put myself on an agency and work that 1 day off in the week?
Yes you can legally do that every week, but remember you must have at-least 9 hours rest before starting the EU in-scope driving job and at-least 9 hours rest after the EU in-scope driving job.
Edit: Also remember that when driving in-scope of EU regulations you will need to carry with you a record of your hours in your usual job, legally these records can be a log book (if you use one) or records hand written on a printout or chart, although it seems the DVSA will accept records written in a diary or notebook.
You only need to record the start and finish times for your usual job as it’s only so the DVSA can see that you’ve complied with the daily and weekly rest period requirements should you get pulled into a roadside spot check.