My experience over 30 months is this;

a. First on the cabinet according to the engineer: 104.2Mbps max attainable.

b. Fell slowly over 2 years to 93Mbps.

c. Lift and shift in March 14 - dropped to 84Mbps.

d. Two periods of maintenance last week and a fault requiring an exchange line card change: downstream speed has dropped to 80.6Mbps.

According to GUI, I am still on Fastpath, INP 0 and no interleaving.

In reply to a post by MrSaffron:

Appliances with the full Kite/CE marking can still cause problems too, i.e. the marks are only from a sample that is tested, a bad batch or single poor solder joint can cause issues.

It's worse than that. All these quality frameworks have the concept of self-certification. If inadequate quality most likely wouldn't directly cause death or serious injury then it's not worth the time and expense to insist on oversight - so the manufacturer applies the mark on their own authority and the first time an independent assessor would check it is if there's a formal complaint. Until / unless that happens to them nothing stops makers or importers fixing the mark without doing any tests at all. Of course if they get caught they could get a fine or even do time, but that's not likely. EM shielding is definitely the sort of thing cut price manufacturers won't test properly even on a sample item.

Not every kind of CE mark can rely on self-certification, a CE marked pacemaker for example has to be tested by an independent third party, but "low risk" things like a beer fridge or a mobile phone charger are usually self certified and thus their quality is indeterminate. You are of course entitled to a full refund if you buy something that's unfit or not as described - and a CE marked item that wouldn't actually pass qualifies as both - but in my experience on very cheap unbranded junk where the problems are most likely people throw it out when they notice a problem rather than trying to get a refund.