Looks like the issues are back - I noticed it got better overnight and has become progressively worse during this morning 
Hmmm. OK here, so far, on Telehouse North, Juniper 1.
I have been experiencing DNS-type problems intermittently for - I would say - a few weeks now. At first I put it down to some new enterprise software rolled out by my employers (it's a work laptop), but the more time goes on, the more I think it's not that.
It's not every day, or even every week, which surely it would be, if it was down to something that had altered at this end.
And I notice it almost exclusively from late afternoons onwards, never in the mornings.
I thought maybe exchange congestion, but the symptoms suggest connectivity issues, NOT speed. If I do a speedtest during one of the affected periods (if I am lucky enough to be able to connect to a speedtest), it will typically show I am getting average, or even better than average speeds.