Two identical laptops, one is able to read a DVD, the other not.
Hardware is fine, it's just that it doesn't recognise the disc.
I've used the Microsoft diagnostics tool, but it can't fix it.
Drivers are up to date.
Any ideas?

HEEEEELP!

Sounds to me like the hardware is not fine. They can be tempramental sods with DVD make, colour and type all adding variables that can throw it. The hardware isn't necessarily identical either. The only other thing I can think of is that the country setting for a video DVD may be wrong so check that if you can.

Can you swap the DVD drives between laptops – sometimes they are designed to be removeable – small lever on one side?

Damn: Talk Talk suspected of dropped connection double post gaffe!

cheers, DVD drive is internal slot loading drive so not easy to access/ remove

What DeVs said, basically. If it's a DVD-R disc then it's down to tolerances, you can get discs that work in some drives but not others. If it's an pre-recorded disc then it could be that the drive is slightly 'out' in some way, or might be slightly less tolerant of flaws and scratches than the other one.

Obvious question perhaps but, have you tried cleaning the disc?

I wiped it on my t-shirt…
will one of those lens cleaning DVDs with the little brush on work? maybe there's dust on the lens or something.

I've given up.
Used a workaround.