is there any issue with overspecing the lead by using 2.5mm² 3 Core?
Not really but it can be a bit of a sod fitting the cable into 13A plugs and extension sockets. I'd just stick with 1.5mm cable personally as the voltage drop isn't likely to be an issue.
I need an extension lead for a freezer. Other than cost and physical flexibility, is there any issue with overspecing the lead by using 2.5mm² 3 Core?
And as a follow-up, is there any knock on implications for the plug and socket for the lead?
Cheers.