This time its myself as a stupid client:
I went to my DSL providers home page and discovered that they doubled the download speed of my service package. I said woohoo and started to check - the speed was still the same. I called support - they said it should be double, but they'd check. A tech called back and let me do a series of download tests from my computer. Then they rebooted the switch. Then they thought that it might be the noise filter thats faulty. I remember saying repeatedly that i am not a noob, but a tech nerd so dont come to teach me how to reboot the DSL modem et al.
Finally i logged into my router and discovered that i had put bandwidth shaping on about the year earlier and it capped the download speed.