Turns out my car needs a new engine, not a replacement sensor....

jimjames

Iceweasel said:

If it's a brand spanking new engine it may have come with a blank space for the technicians to copy/stamp the original number.

It would seem very unlikely that a non dealership garage would fit a brand new engine in an 11 year old car that cost £4k but I guess it depends who did the work.

KPM2019 said:

I do wonder if they have replaced it with a battered old engine that's done 100k+ miles. Where do I stand if that's the case? How will I be able to check? I think IF I get it back, my first call should be the garage for a full check to see what's what. 

I think at this stage any working engine is better than what was in your car. It also demonstrates that a low mileage engine isn't necessarily a good thing so high mileage well maintained could be better.

KPM2019

Right then, I received an email this morning from the dealer, after one yesterday telling me the car was ready for collection. I asked whether the warranty was for 6 or 12 months (as previously told that's what it would be) and had a reply to say that the replacement engine comes with a 30 day Internals only guarantee and they recommend I purchase their 15 month warranty for peace of mind at £425. 
They have sent me the engine details 

Peugeot 208 MK1 1.0 Petrol Bare Engine 2012 - 2019 EB0 (ZMZ) / 1608512180 14K Miles