Thanks for your quick replies, Camieabz and ultra. I'm glad I looked into this, as I almost signed up to an 18 month contract that would have been slower for everything I do except browsing.
I'm glad I read those links you gave. At PlusNet's 'Traffic Management Key Facts'
for Plusnet Value Fibre (the package I was interested in) it seems just about everything apart from browsing, audio streaming, VoIP and IM (neither of which I use) are crippled in the evenings.
I'm currently on O2 Home Broadband Standard, which is unlimited and I've never noticed any
traffic shaping. I just tested my speed and got 9Mbps down, 1.03 up. It never
drops below 6.5Mbps down.
The page download speed
shows I would get far slower speeds on fibre for everything apart from browsing except during the night (when I'm asleep), so I'd be silly to change. I appear to be on the best package for my needs.
It looks like my obsolete copper ADSL is quicker than superfast fibre!