At this age and mileage, there are too many variables to give sensible advice either way.

Older diesels can give problems and much will depend on how they have been treated and maintained earlier in life.

The most important thing is to base your decision on condition and traceable service history. Old bills and invoices to back up the service manual would be good. Try and speak to previous owners. If a car dealer starts spouting Data Protection Act, walk away.

On the face if it, an Accord should be more reliable, but condition and history are all important. If you do go for a Mondeo, the 2.0 TDCi is a much better engine than the 1.8.

Have owned both and this is just my personal experience

Mondeo tdci 2.0

Great driving car but had to replace 4 injectors (not all at once)Starter motor broke up and poisioned fuel delivery system . Car scrapped as a result

This was a pre face lift model and think they sorted the starter motor issue in the facelif. The 2.0 tdci engine is a super reliable engine but (as with all modern diesels trying to balance ecomony and power) there are many fuel delivery, flywheel and drivetrain issues

If ur gonna go ford go for the 2.0tdci mk 3 facelight

Accord

I currently have an accord ctdi and its the best diesel iv had in terms of performance. Honda diesel very smooth (take off in second gear)

It really is a much better car than the mk3 mondeo in terms of reliability but here are the main issues

Prefacelift models. Possible chaincam failure. All Needd to have a history of using the correct honda oil. 03/04 can have manifold problems. Opting for the facelift model should erradicate these issues

But. Clutch will fail as there is an issue with it and will need a new flywheel when it does. Also driveshafts are prone to failure.

In summary though and as stated I have come to the conclusion that all modern diesel have thete own issues but the mondeo will have 3 times the issues of the accord. The accord will cost more too though. Good luck. (Ps noidea why text size kept changing on me as using my phone here)