Fairly common practice these days for Charter airlines to get crews to operate out and deadhead back on the same aircraft, commonly a end of season thing. OK it might not be nice roading it to CWL and then paxing for a total of 19 hrs but its again a fairly common practice for "lean and mean" Companies.
Something that happens at MON all the time, although the current CC are getting plenty of support to change this unreasonable and quite frankly morally corrupt practice.
Don't forget that your vehicle insurer as well as the CPS would take a dim view if you had an injury causing accident, and it could be proved you have been on duty for an excessive length of time.