LCCs make as much out of late bookings as they do out of holding early bookings for months. There are no such things as Stand By and all carriers continue to hold the line that they will not sell of empty seats at bucket rates in the last 5 minutes before closing. They know what that would do to future bookings.
You may meet the law of diminishing returns and best to cut your losses and run. If you have to get back to start looking for work, then the sooner you are back the better. If you have free accommodation in the UK but not in France, then the extra flight cost is offset.