So, we collected the car last night and it seems it was a combination of two things.
First, the last (?) batch of fuel we got was very dirty.
Second, the filter needed to be changed.
The guy drained the tank and put some cleaner in it, put more fuel in and changed the filter.
He drove it around and tested it with no problems - although he did say it would take a little while to completely clear up and it would sometimes feel underpowered.
The alternative, assuming the above did not work, was some sort of electronic box that was going to set us back €500.
The 15km drive home showed no problems. Unfortunately, this morning the car was sluggish and the EMS light came back on...
The guy at the garage did do a diagnostic check with the computer and came up with no problems so what can it be?