Well technically you still fall under Working Time Directive rules.
You haven’t said what kind of work the saturday work is.
POA does not count as working time so you can use that to get to 70 hour weeks if you wish. (Personally 70 hours is too much for me)
Weekly rest
Workers have the right to either:an uninterrupted 24 hours without any work each week
an uninterrupted 48 hours without any work each fortnight
Source: gov.uk/rest-breaks-work
However:
Exceptions
Workers aren’t entitled to the 3 general types of rest break if they work in:the armed forces, emergency services or police and they’re dealing with an exceptional catastrophe or disaster
a job where they freely choose what hours they work (like a managing director) or where the work is not measured (ie no set hours)
sea transport
air or road transport (known as ‘mobile’ workers)
Air, sea or road transport workers may be covered by special rules that give them different rest rights.Mobile workers not covered by any special rules usually have the right to regular rest so that their health and safety (or anyone else’s) isn’t put at risk.
There are also special rules for young workers and for lorry and coach drivers.
Source: gov.uk/rest-breaks-work/exceptions
In theory your employer is supposed to manage WTD to make sure you have enough rest each week - I don’t believe DVSA/VOSA etc enforce those rules.